Expat through 2.8.3 contains an out-of-bounds read vulnerability that allows attackers to trigger memory corruption by processing XML with external entity parsers created via XML_ExternalEntityParserCreate. A struct size mismatch between ELEMENT_TYPE members causes storeAtts to read the attIndex member past allocated memory boundaries, resulting in failure to normalize whitespace in non-CDATA attributes or a wild pointer dereference causing a segfault. This vulnerability was introduced by the fix for CVE-2026-66046.

The version of FreeBSD installed on the remote host is prior to tested version. It is, therefore, affected by a vulnerability as referenced in the 11ab3b16-a65d-11f1-a49c-00a0980083d7 advisory.

    https://github.com/libexpat/libexpat/pull/1331 reports:
    Expat through 2.8.3 contains an out-of-bounds read vulnerability             that allows attackers to trigger memory corruption by processing             XML with external entity parsers created via             XML_ExternalEntityParserCreate.  A struct size mismatch between             ELEMENT_TYPE members causes storeAtts to read the attIndex member             past allocated memory boundaries, resulting in failure to normalize             whitespace in non-CDATA attributes or a wild pointer dereference             causing a segfault.  This vulnerability was introduced by the fix             for CVE-2026-66046.

Tenable has extracted the preceding description block directly from the FreeBSD security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

There are packages installed that are affected by multiple vulnerabilities referenced in the following CVEs:

  - 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. (CVE-2026-66046)

  - Expat through 2.8.3 contains an out-of-bounds read vulnerability that allows attackers to trigger memory
    corruption by processing XML with external entity parsers created via XML_ExternalEntityParserCreate. A
    struct size mismatch between ELEMENT_TYPE members causes storeAtts to read the attIndex member past
    allocated memory boundaries, resulting in failure to normalize whitespace in non-CDATA attributes or a
    wild pointer dereference causing a segfault. This vulnerability was introduced by the fix for
    CVE-2026-66046. (CVE-2026-76641)

  - In libexpat 2.8.2 and 2.8.3 before 2.8.4, misinterpretation of getentropy's return code leads to
    insufficient entropy, which results in being vulnerable to hash flooding attacks, causing a denial of
    service via crafted XML content. (CVE-2026-76956)

  - 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.
    (CVE-2026-76957)

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - Expat through 2.8.3 contains an out-of-bounds read vulnerability that allows attackers to trigger memory     corruption by processing XML with external entity parsers created via XML_ExternalEntityParserCreate. A     struct size mismatch between ELEMENT_TYPE members causes storeAtts to read the attIndex member past     allocated memory boundaries, resulting in failure to normalize whitespace in non-CDATA attributes or a     wild pointer dereference causing a segfault. This vulnerability was introduced by the fix for     CVE-2026-66046. (CVE-2026-76641)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
342351	FreeBSD : expat2 -- Out-of-bounds Read (11ab3b16-a65d-11f1-a49c-00a0980083d7)	Nessus	FreeBSD Local Security Checks	Local	high
447379	Alpine: libexpat, multiple expat packages: security update to 2.8.4-r0	Tenable Cloud Security	Alpine Linux Local Security Checks	Local	high
447379	Alpine: libexpat, multiple expat packages: security update to 2.8.4-r0	Tenable Self-Hosted Container Security	Alpine Linux Local Security Checks	Local	high
338716	Linux Distros Unpatched Vulnerability : CVE-2026-76641	Nessus	Misc.	Local	high

Detections

Analytics

CVE-2026-76641

high

Tenable Plugins

high

high

high

high