CVE-2025-6069

The html.parser.HTMLParser class had worse-case quadratic complexity when processing certain crafted malformed inputs potentially leading to amplified denial-of-service.

Weakness

The product uses a regular expression with an inefficient, possibly exponential worst-case computational complexity that consumes excessive CPU cycles.

Affected Software

Extended Description

	  Attackers can create crafted inputs that
	  intentionally cause the regular expression to use
	  excessive backtracking in a way that causes the CPU
	  consumption to spike.

Potential Mitigations

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/492.html

References

• https://github.com/python/cpython/commit/4455cbabf991e202185a25a631af206f60bbc949
• https://github.com/python/cpython/commit/6eb6c5dbfb528bd07d77b60fd71fd05d81d45c41
• https://github.com/python/cpython/commit/8d1b3dfa09135affbbf27fb8babcf3c11415df49
• https://github.com/python/cpython/commit/ab0893fd5c579d9cea30841680e6d35fc478afb5
• https://github.com/python/cpython/commit/d851f8e258c7328814943e923a7df81bca15df4b
• https://github.com/python/cpython/commit/f3c6f882cddc8dc30320d2e73edf019e201394fc
• https://github.com/python/cpython/commit/fdc9d214c01cb4588f540cfa03726bbf2a33fc15
• https://github.com/python/cpython/issues/135462
• https://github.com/python/cpython/pull/135464
• https://mail.python.org/archives/list/security-announce@python.org/thread/K5PIYLR6EP3WR7ZOKKYQUWEDNQVUXOYM/