CVE-2025-4516

There is an issue in CPython when using bytes.decode(unicode_escape, error=ignore|replace). If you are not using the unicode_escape encoding or an error handler your usage is not affected. To work-around this issue you may stop using the error= handler and instead wrap the bytes.decode() call in a try-except catching the DecodeError.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://github.com/python/cpython/commit/4398b788ffc1f954a2c552da285477d42a571292
• https://github.com/python/cpython/commit/6279eb8c076d89d3739a6edb393e43c7929b429d
• https://github.com/python/cpython/commit/69b4387f78f413e8c47572a85b3478c47eba8142
• https://github.com/python/cpython/commit/73b3040f592436385007918887b7e2132aa8431f
• https://github.com/python/cpython/commit/8d35fd1b34935221aff23a1ab69a429dd156be77
• https://github.com/python/cpython/commit/9f69a58623bd01349a18ba0c7a9cb1dad6a51e8e
• https://github.com/python/cpython/commit/ab9893c40609935e0d40a6d2a7307ea51aec598b
• https://github.com/python/cpython/issues/133767
• https://github.com/python/cpython/pull/129648
• https://mail.python.org/archives/list/security-announce@python.org/thread/L75IPBBTSCYEF56I2M4KIW353BB3AY74/
• http://www.openwall.com/lists/oss-security/2025/05/16/4
• http://www.openwall.com/lists/oss-security/2025/05/19/1