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gh-95778: CVE-2020-10735: Prevent DoS by very large int() (#96499)

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Integer to and from text conversions via CPython's bignum `int` type is not safe against denial of service attacks due to malicious input. Very large input strings with hundred thousands of digits can consume several CPU seconds.

This PR comes fresh from a pile of work done in our private PSRT security response team repo.

Signed-off-by: Christian Heimes [Red Hat] <christian@python.org>
Tons-of-polishing-up-by: Gregory P. Smith [Google] <greg@krypto.org>
Reviews via the private PSRT repo via many others (see the NEWS entry in the PR).

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

I wrote up [a one pager for the release managers](https://docs.google.com/document/d/1KjuF_aXlzPUxTK4BMgezGJ2Pn7uevfX7g0_mvgHlL7Y/edit#). Much of that text wound up in the Issue. Backports PRs already exist. See the issue for links.
This commit is contained in:
Gregory P. Smith 2022-09-02 09:35:08 -07:00 • committed by GitHub
parent 656167db81
commit 511ca94520
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28 changed files with 803 additions and 20 deletions
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8
Lib/test/test_ast.py
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@ -1136,6 +1136,14 @@ Module(
self.assertRaises(ValueError, ast.literal_eval, '+True')
self.assertRaises(ValueError, ast.literal_eval, '2+3')
def test_literal_eval_str_int_limit(self):
with support.adjust_int_max_str_digits(4000):
ast.literal_eval('3'*4000) # no error
with self.assertRaises(SyntaxError) as err_ctx:
ast.literal_eval('3'*4001)
self.assertIn('Exceeds the limit ', str(err_ctx.exception))
self.assertIn(' Consider hexadecimal ', str(err_ctx.exception))
def test_literal_eval_complex(self):
# Issue #4907
self.assertEqual(ast.literal_eval('6j'), 6j)