Vulnerabilities

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.

libexpat before 2.8.2 has an integer overflow in copyString.

In libexpat before 2.8.2, there is a heap-based buffer overflow in doProlog in xmlparse.c because scaffold backing array reallocation is mishandled when there is data-structure sharing across parsers.

libexpat before 2.8.2 lacks handler call depth tracking for calls to XML_GetBuffer, XML_Parse, XML_ParseBuffer, XML_ParserFree, or XML_ParserReset from within handlers in cases of a policy violation. Thus, a use-after-free can occur,

In libexpat before 2.8.1, the computational complexity of attribute name collision checks allows a denial of service via moderately sized crafted XML input.

libexpat before 2.8.0 uses insufficient entropy, and thus hash flooding can occur via a crafted XML document.

libexpat before 2.7.5 allows an infinite loop while parsing DTD content.

In libexpat before 2.7.4, the doContent function does not properly determine the buffer size bufSize because there is no integer overflow check for tag buffer reallocation.

In libexpat before 2.7.4, XML_ExternalEntityParserCreate does not copy unknown encoding handler user data.

In libexpat through 2.7.3, a crafted file with an approximate size of 2 MiB can lead to dozens of seconds of processing time.

libexpat in Expat before 2.7.2 allows attackers to trigger large dynamic memory allocations via a small document that is submitted for parsing.

An issue was discovered in libexpat before 2.6.4. There is a crash within the XML_ResumeParser function because XML_StopParser can stop/suspend an unstarted parser.

An issue was discovered in libexpat before 2.6.3. nextScaffoldPart in xmlparse.c can have an integer overflow for m_groupSize on 32-bit platforms (where UINT_MAX equals SIZE_MAX).

libexpat through 2.6.1 allows an XML Entity Expansion attack when there is isolated use of external parsers (created via XML_ExternalEntityParserCreate).

libexpat through 2.5.0 allows a denial of service (resource consumption) because many full reparsings are required in the case of a large token for which multiple buffer fills are needed.

In libexpat through 2.4.9, there is a use-after free caused by overeager destruction of a shared DTD in XML_ExternalEntityParserCreate in out-of-memory situations.

libexpat before 2.4.9 has a use-after-free in the doContent function in xmlparse.c.

In Expat (aka libexpat) before 2.4.5, there is an integer overflow in storeRawNames.

xmlparse.c in Expat (aka libexpat) before 2.4.5 allows attackers to insert namespace-separator characters into namespace URIs.

Expat (aka libexpat) before 2.4.4 has an integer overflow in the doProlog function.

Expat (aka libexpat) before 2.4.4 has a signed integer overflow in XML_GetBuffer, for configurations with a nonzero XML_CONTEXT_BYTES.

addBinding in xmlparse.c in Expat (aka libexpat) before 2.4.3 has an integer overflow.

In doProlog in xmlparse.c in Expat (aka libexpat) before 2.4.3, an integer overflow exists for m_groupSize.

In Expat (aka libexpat) before 2.4.3, a left shift by 29 (or more) places in the storeAtts function in xmlparse.c can lead to realloc misbehavior (e.g., allocating too few bytes, or only freeing memory).

In libexpat before 2.2.8, crafted XML input could fool the parser into changing from DTD parsing to document parsing too early; a consecutive call to XML_GetCurrentLineNumber (or XML_GetCurrentColumnNumber) then resulted in a heap-based buffer over-read.

In libexpat in Expat before 2.2.7, XML input including XML names that contain a large number of colons could make the XML parser consume a high amount of RAM and CPU resources while processing (enough to be usable for denial-of-service attacks).