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update_email() validated the new email against
^([0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*@{1}([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})$,
a pattern with nested, overlapping quantifiers - classic catastrophic
backtracking territory. A crafted input (many repeated characters
followed by a non-matching character) can drive the regex engine's
running time up exponentially, tying up a request-handling thread
indefinitely.
The code already had a correct, backtracking-safe regex behind the
`vuln` flag's else branch - made that the only path (as a raw string,
which also silently fixes a pre-existing SyntaxWarning from the
unescaped `\.` in the old non-raw string literal).
Verified live: a normal email update still succeeds (204); a
40-character repeated-character-plus-non-matching-suffix payload that
would catastrophically backtrack against the old pattern now returns
in ~10ms with a 400 "invalid email" response instead of hanging.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
🏆 VAmPI — CTF Patch Score1 / 9 challenges patched
Commit: 🎉 Your result is on the leaderboard — see where you rank! 🏆 |
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Summary
update_email()validated the new email against a regex with nested, overlapping quantifiers - classic catastrophic-backtracking territory, letting a crafted input tie up a request thread indefinitely. Switched to the already-present backtracking-safe pattern (previously gated behind thevulnflag).Test plan