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May 2025

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[CVE-2025-4516] Use-after-free crash using bytes.decode("unicode_escape", error="ignore|replace")
by Seth Larson May 15, 2025

May 15, 2025

There is a MEDIUM severity security issue in CPython when using `bytes.decode("unicode_escape", error="ignore|replace")`. The use-after-free being exploited would likely result in a crash. 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 decoding error. Please see the linked CVE ID for the latest information on affected versions: * https://www.cve.org/CVERecord?id=CVE-2025-4516 * https://github.com/python/cpython/pull/129648

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