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[3.7] gh-95778: CVE-2020-10735: Prevent DoS by very large int() by gpshead · Pull Request #96504 · python/cpython

and others added 13 commits

September 1, 2022 17:42
This is required for the 3.7 tree to pass on modern macOS.
I don't know why, but macOS in 3.7 CI is failing to build the zlib
module these days so it's exposing this test that didn't have the
proper `@requires_zlib` annotation.

Getting it to build with zlib and other things that are now wrongly
"missing" in the 3.7 CI setup would be nice, but probably involves
invasive backporting of parts of
python@b29d0a5
by a macOS domain expert.

Not worth it.
This test also appears to require changes to
Lib/ctypes/macholib/dyld.py to work in the existing macOS CI config.
I'm just skipping it, backporting that would be a feature.
Not going to happen in 3.7.

There may be a way to configure macOS CI to use an older macOS and
toolchain instead as an alternate option.  Someone else can figure
that out if so.  This branch only lives for another 9 months per
https://peps.python.org/pep-0537/
the 3.8 branch got rid of this line already.  it blocks seeing the
actual error while testing a doc build!

zooba

…#96537)

Converting a large enough `int` to a decimal string raises `ValueError` as expected. However, the raise comes _after_ the quadratic-time base-conversion algorithm has run to completion. For effective DOS prevention, we need some kind of check before entering the quadratic-time loop. Oops! =)

The quick fix: essentially we catch _most_ values that exceed the threshold up front. Those that slip through will still be on the small side (read: sufficiently fast), and will get caught by the existing check so that the limit remains exact.

The justification for the current check. The C code check is:
```c
max_str_digits / (3 * PyLong_SHIFT) <= (size_a - 11) / 10
```

In GitHub markdown math-speak, writing $M$ for `max_str_digits`, $L$ for `PyLong_SHIFT` and $s$ for `size_a`, that check is:
$$\left\lfloor\frac{M}{3L}\right\rfloor \le \left\lfloor\frac{s - 11}{10}\right\rfloor$$

From this it follows that
$$\frac{M}{3L} < \frac{s-1}{10}$$
hence that
$$\frac{L(s-1)}{M} > \frac{10}{3} > \log_2(10).$$
So
$$2^{L(s-1)} > 10^M.$$
But our input integer $a$ satisfies $|a| \ge 2^{L(s-1)}$, so $|a|$ is larger than $10^M$. This shows that we don't accidentally capture anything _below_ the intended limit in the check.

<!-- gh-issue-number: pythongh-95778 -->
* Issue: pythongh-95778
<!-- /gh-issue-number -->

Co-authored-by: Gregory P. Smith [Google LLC] <greg@krypto.org>

ypankovych

stratakis pushed a commit to stratakis/cpython that referenced this pull request

Mar 11, 2024
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)

stratakis pushed a commit to stratakis/cpython that referenced this pull request

Mar 11, 2024
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)

stratakis pushed a commit to stratakis/cpython that referenced this pull request

Mar 20, 2024
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)

stratakis pushed a commit to stratakis/cpython that referenced this pull request

Mar 20, 2024
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)

stratakis pushed a commit to stratakis/cpython that referenced this pull request

Mar 20, 2024
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)

stratakis pushed a commit to stratakis/cpython that referenced this pull request

Mar 20, 2024
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)

stratakis pushed a commit to stratakis/cpython that referenced this pull request

Mar 25, 2024
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)

hroncok pushed a commit to fedora-python/cpython that referenced this pull request

Mar 26, 2024
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)

mcepl pushed a commit to openSUSE-Python/cpython that referenced this pull request

Apr 2, 2024
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)

hrnciar pushed a commit to fedora-python/cpython that referenced this pull request

Apr 23, 2025
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)

hroncok pushed a commit to fedora-python/cpython that referenced this pull request

Jul 4, 2025
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)

frenzymadness pushed a commit to fedora-python/cpython that referenced this pull request

Aug 12, 2025
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)

hroncok pushed a commit to fedora-python/cpython that referenced this pull request

Feb 3, 2026
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)