gh-146333: Fix quadratic regex backtracking in configparser option parsing - #146399
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encukou merged 2 commits intoApr 7, 2026
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joshuaswanson
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| # Compiled regular expression for matching sections | ||
| SECTCRE = re.compile(_SECT_TMPL, re.VERBOSE) | ||
| # Compiled regular expression for matching options with typical separators | ||
| OPTCRE = re.compile(_OPT_TMPL.format(delim="=|:"), re.VERBOSE) |
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This is safe because the option name is already stripped via .rstrip() in _handle_option (line 1160), and the value is stripped via .strip() (line 1169).
The regexes are publicly exposed, this breaks it for people who use them directly.
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Good point, thanks. Updated to keep the regexes unchanged. Instead, |
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Overriding Would it work to add negative lookahead, @joshuaswanson, please don't force-push to CPython PR branches -- it makes the changes a little harder to follow for reviewers, and every PR gets squashed anyway. |
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Won't force-push again, sorry about that. The simple The fix restructures the option group to |
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This looks good, thank you! |
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The issue was tagged with "security". Should we backport this change to all supported Python versions (3.10-3.14)? |
encukou
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needs backport to 3.10
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Thanks @joshuaswanson for the PR, and @encukou for merging it 🌮🎉.. I'm working now to backport this PR to: 3.10. |
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Yes. |
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Thanks @joshuaswanson for the PR, and @encukou for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11. |
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Thanks @joshuaswanson for the PR, and @encukou for merging it 🌮🎉.. I'm working now to backport this PR to: 3.12. |
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Thanks @joshuaswanson for the PR, and @encukou for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13. |
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Thanks @joshuaswanson for the PR, and @encukou for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14. |
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Sorry, @joshuaswanson and @encukou, I could not cleanly backport this to |
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Sorry, @joshuaswanson and @encukou, I could not cleanly backport this to |
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Sorry, @joshuaswanson and @encukou, I could not cleanly backport this to |
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Sorry, @joshuaswanson and @encukou, I could not cleanly backport this to |
miss-islington
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Apr 9, 2026
…ion parsing (pythonGH-146399) Use negative lookahead in option regex to prevent backtracking, and to avoid changing logic outside the regexes (since people could use the regex directly). (cherry picked from commit 7e0a0be) Co-authored-by: Joshua Swanson <22283299+joshuaswanson@users.noreply.github.com>
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GH-148287 is a backport of this pull request to the 3.14 branch. |
| parser = configparser.RawConfigParser() | ||
| content = "[section]\n" + "x" + " " * 40000 + "y" + "\n" | ||
| # This should complete almost instantly. Before the fix, | ||
| # it would take over a minute due to catastrophic backtracking. |
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On my system it takes ~8 seconds, I suggest increasing it in backports to a larger number of whitespace, as 8 seconds is short enough that it could be missed.
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A minute could be missed as well :/
I'm afraid this is fuzzer material; our tests can't quite do time complexity checking.
gpshead
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Apr 12, 2026
…tion parsing (GH-146399) (#148287) gh-146333: Fix quadratic regex backtracking in configparser option parsing (GH-146399) Use negative lookahead in option regex to prevent backtracking, and to avoid changing logic outside the regexes (since people could use the regex directly). (cherry picked from commit 7e0a0be) Co-authored-by: Joshua Swanson <22283299+joshuaswanson@users.noreply.github.com>
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GH-148559 is a backport of this pull request to the 3.13 branch. |
encukou
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Apr 14, 2026
…ser option parsing (pythonGH-146399) Use negative lookahead in option regex to prevent backtracking, and to avoid changing logic outside the regexes (since people could use the regex directly). (cherry picked from commit 7e0a0be) Co-authored-by: Joshua Swanson <22283299+joshuaswanson@users.noreply.github.com>
encukou
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Apr 15, 2026
…tion parsing (GH-146399) (GH-148559) Use negative lookahead in option regex to prevent backtracking, and to avoid changing logic outside the regexes (since people could use the regex directly). (cherry picked from commit 7e0a0be) Co-authored-by: Joshua Swanson <22283299+joshuaswanson@users.noreply.github.com>
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ljfp
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Apr 25, 2026
…ion parsing (pythonGH-146399) Use negative lookahead in option regex to prevent backtracking, and to avoid changing logic outside the regexes (since people could use the regex directly).
Yhg1s
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Aug 4, 2026
…tion parsing (GH-146399) (GH-148559) (#154081) Use negative lookahead in option regex to prevent backtracking, and to avoid changing logic outside the regexes (since people could use the regex directly). (cherry picked from commit 7e0a0be) (cherry picked from commit a5969e8) Co-authored-by: Joshua Swanson <22283299+joshuaswanson@users.noreply.github.com>
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The
_OPT_TMPLand_OPT_NV_TMPLregexes have quadratic backtracking when a line contains many spaces between non-delimiter characters. The lazy.*?in the option group and the\s*before the delimiter overlap on whitespace, so the engine tries every possible split point.The fix removes
\s*before the delimiter. This is safe because the option name is already stripped via.rstrip()in_handle_option(line 1160), and the value is stripped via.strip()(line 1169).Before:
x+ 40000 spaces +ytakes ~86 secondsAfter: ~0.004 seconds
configparser.RawConfigParser.{OPTCRE,OPTCRE_NV}regexes vulnerable to quadratic backtracking #146333