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CVE-2026-76875: PyPy pyexpat ExternalEntityParserCreate Use-After-Free

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-29 · updated 2026-10-02
• Weakness: CWE-416

Description

PyPy before versions 3.11.16 and 3.12.14 contains a use-after-free vulnerability in the pyexpat module's ExternalEntityParserCreate function that allows attackers to corrupt memory by supplying a crafted XML document to applications that create external-entity sub-parsers without retaining a reference to the parent parser. The child parser retains a raw C back-pointer to the parent parser struct while PyPy's tracing garbage collector can free the parent's C struct, causing bundled libexpat to dereference the freed pointer on every parsed token, producing memory corruption.

Affected products

• PyPy: before 3.11.16; from 3.12.0 before 3.12.14 — fixed in 3.11.16, 3.12.14

How to fix

Upgrade to a fixed version: PyPy 3.11.16, 3.12.14. Check the vendor advisory for mitigations.

References

• https://doc.pypy.org/release-v8.0.0.html
• https://github.com/pypy/pypy/releases/tag/release-pypy3.11-v8.0.0
• https://github.com/pypy/pypy/releases/tag/release-pypy3.12-v8.0.0
• https://www.vulncheck.com/advisories/pypy-pyexpat-externalentityparsercreate-use-after-free

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