libexpat Parser Memory Safety Vulnerabilities

Heap-based buffer overflow in libexpat before 2.8.2 allows heap memory corruption in applications that process externally-supplied XML with external entity parameter parsing enabled. The flaw resides in the doProlog function of xmlparse.c, where the scaffold backing array (scaffIndex) - used to index DTD content model tree nodes - is reallocated using the child parser's m_groupSize counter, which diverges from the actual allocated capacity of the shared scaffIndex inherited from the parent parser. No public exploit code has been identified and the vulnerability is not listed in CISA KEV at time of analysis, but the upstream fix PR includes a functional reproduction test case confirming exploitability.

Use-after-free in libexpat before 2.8.2 allows memory corruption when XML_ResumeParser is called from within a handler callback during a policy-violation scenario. The missing call-depth guard permits re-entrant parser invocation, leaving dangling pointers in the parser's internal heap state and enabling potential information disclosure or memory corruption with low confidentiality, integrity, and availability impact. No public exploit is identified at time of analysis, and the high attack complexity (AC:H) reflects the specific re-entrant handler pattern required to trigger the flaw.