CVE-2026-56131

An issue was discovered in libexpat before 2.6.3, where xmlparse.c does not reject a negative length for XML_ParseBuffer.

The writeRandomBytes_RtlGenRandom function in xmlparse.c in libexpat versions 2.2.1 and 2.2.2 on Windows allows local users to gain privileges via a Trojan horse ADVAPI32.DLL in the current working directory due to an untrusted search path, known as DLL hijacking.

XML External Entity vulnerability in libexpat 2.2.0 and earlier allows attackers to put the parser in an infinite loop using a malformed external entity definition from an external DTD.

Issue in libexpat before version 2.6.4. The XML_ResumeParser function can crash if XML_StopParser stops/suspends an unstarted parser.

An issue was discovered in libexpat before version 2.6.3, which can lead to an integer overflow in the nextScaffoldPart function in xmlparse.c on 32-bit platforms.

An issue was discovered in libexpat before version 2.6.3 related to integer overflow in the dtdCopy function in xmlparse.c. This issue occurs on 32-bit platforms where UINT_MAX equals SIZE_MAX.

libexpat before 2.8.4 lacks handler call depth tracking with custom encoding callbacks. Thus, a use-after-free can occur. NOTE: this is similar to CVE-2026-50219, CVE-2026-56131 and CVE-2026-56412.

In libexpat versions 2.8.2 and 2.8.3 before 2.8.4, misinterpretation of getentropy's return code leads to insufficient entropy, making it vulnerable to hash flooding attacks, causing denial of service via crafted XML content.

libexpat before 2.8.3 has an out-of-bounds read and resultant infinite loop because low surrogates are treated the same as high surrogates during Unicode processing in the *_toUtf16 functions.

In libexpat before version 2.8.2, XML_TOK_DATA_CHARS is not considered in doCdataSection, leading to a lack of handler call depth tracking in cases of policy violation. This can result in a use-after-free error.