libexpat xmlwf through 2.10.0 Symlink Following via -d Output Directory

The xmlwf tool in libexpat through 2.10.0 contains a symlink following vulnerability because -d output mode opens files with fopen("wb"), which follows symbolic links. Local attackers with write access to the output directory can plant a symlink at the expected output name to truncate or overwrite files writable by the xmlwf user.

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 unknown_toUtf8() and unknown_toUtf16() 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.

Expat before 2.8.5 Malformed UTF-16 Acceptance via Unchecked Surrogate

Expat before 2.8.5 fails to validate that a high surrogate in UTF-16 input is followed by a low surrogate, allowing malformed UTF-16 sequences to be accepted. Attackers can supply UTF-16 encoded XML containing lone high surrogates that consume the following code unit, causing Expat to pass unpaired surrogates to applications built with XML_UNICODE and to silently replace input characters in other builds.

libexpat Heap Buffer Over-read in xmlparse.c via XML_ParseBuffer

libexpat before commit 13c5f63 contains a heap buffer over-read vulnerability in xmlparse.c. XML_ParseBuffer advances the parse buffer end with parser->m_bufferEnd += len using a caller-supplied length that is not validated against the allocated buffer size, so repeated XML_ParseBuffer calls move m_bufferEnd past the end of the heap allocation and subsequent parsing reads out of bounds. Reaching this path requires a parse buffer to already be present; otherwise XML_ParseBuffer returns XML_ERROR_NO_BUFFER. A buffer is present after a prior call to XML_GetBuffer, either directly (the common case) or indirectly through a prior XML_Parse call that allocates the buffer internally. The over-read discloses adjacent heap memory to the calling application, recovering heap pointers, libc function pointers, and code pointers sufficient to defeat ASLR and build further exploitation primitives.

libexpat: libexpat: Memory corruption vulnerability allows arbitrary code execution or denial of service

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.

expat: libexpat: Denial of Service due to incorrect Unicode surrogate handling

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.

Expat Denial of Service via storeAtts() Quadratic Complexity

Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified attributes with non-normalized values triggers an O(N^2) linear scan of elementType->defaultAtts to determine CDATA status. A remote unauthenticated attacker can supply a single well-formed XML document of a few megabytes to an application parsing untrusted XML to cause excessive CPU consumption, resulting in denial of service without requiring authentication, external entity resolution, or non-default parser options.

libexpat: libexpat: Use-after-free vulnerability due to improper handling of XML CDATA sections

libexpat before 2.8.2 does not consider XML_TOK_DATA_CHARS in doCdataSection and thus lacks handler call depth tracking for various calls from within handlers in cases of a policy violation. Thus, a use-after-free can occur. NOTE: this issue exists because of an incomplete fix for CVE-2026-50219.

expat: libexpat: Integer Overflow Vulnerability Leading to Information Disclosure or Code Execution

xmlwf in libexpat before 2.8.2 has an integer overflow in endDoctypeDecl via NOTATION declarations.

libexpat: libexpat: Integer overflow in xmlwf can lead to information disclosure and arbitrary code execution.

xmlwf in libexpat before 2.8.2 has an integer overflow in resolveSystemId.

Integer Overflow in libexpat xmlwf Output File Handling

xmlwf in libexpat before 2.8.2 has an integer overflow for the output filename when -d outputDir is used.

Integer Overflow in libexpat copyString Function

libexpat before 2.8.2 has an integer overflow in copyString.

Integer Overflow in libexpat XML Parser

libexpat before 2.8.2 has an integer overflow in doProlog that is related to storeEntityValue and entity textLen.

libexpat: libexpat: Arbitrary code execution via integer overflow in XML_ParseBuffer

libexpat before 2.8.2 has an integer overflow in XML_ParseBuffer because it lacked a check that was present in XML_Parse.

libexpat: libexpat: Information disclosure and arbitrary code execution via integer overflow

libexpat before 2.8.2 has an integer overflow in getAttributeId.

libexpat before 2.8.2 has an integer overflow in addBinding.

libexpat: libexpat: Arbitrary code execution due to integer overflow in storeAtts

libexpat before 2.8.2 has an integer overflow in storeAtts.

expat: libexpat: Arbitrary Code Execution via Heap-based Buffer Overflow

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.

Use-After-Free in libexpat's XML_ResumeParser Call Depth Tracking

libexpat before 2.8.2 lacks handler call depth tracking for calls to XML_ResumeParser from within handlers in cases of a policy violation. Thus, a use-after-free can occur (similar to the CVE-2026-50219 situation).

expat: libexpat: Use-after-free vulnerability due to improper handler call depth tracking

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,