CVE-2026-124317: libexpat through 2.10.0 Out-of-Bounds Read via unknown_toUtf8 and unknown_toUtf16

libexpat through 2.10.0 contains an out-of-bounds read vulnerability in unknowntoUtf8() and unknowntoUtf16() in xmltok.c when handling application-registered unknown encodings. Attackers can supply a document ending in a truncated multibyte sequence so the convert callback reads past the parse buffer, leaking adjacent memory or crashing applications.