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 Tencent Linux installed on the remote TencentOS Server 4 host is prior to tested version. It is, therefore, affected by a vulnerability as referenced in the TSSA-2026:1058 advisory.

    Package updates are available for TencentOS Server 4 that fix the following vulnerabilities:

    CVE-2026-76641:
    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 Tencent Linux security advisory.

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

The remote SUSE Linux SLES16 / SLES_SAP16 host has packages installed that are affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:23912-1 advisory.

    - CVE-2026-41080: crafted XML document can cause a denial of service (bsc#1262263).
    - CVE-2026-45186: 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 (bsc#1264713).
    - CVE-2026-50219: 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     (bsc#1267631).
    - CVE-2026-56131: libexpat before 2.8.2 lacks handler call depth tracking for calls to XML_ResumeParser     from within       handlers in cases of a policy violation (bsc#1268572).
    - CVE-2026-56132: mishandled memory reallocation during array scaffolding in doProlog can cause heap-based     buffer       overflows (bsc#1268573).
    - CVE-2026-56403: integer overflow in the storeAtts function can cause memory corruption and potential     arbitrary code       execution (bsc#1275096).
    - CVE-2026-56404: integer overflow in the addBinding function can cause undersized memory allocations,     memory       corruption, and application crashes (bsc#1275096).
    - CVE-2026-56405: integer overflow in the getAttributeId function can cause heap memory corruption and     arbitrary       code execution (bsc#1275096).
    - CVE-2026-56406: missing bounds validation in XML_ParseBuffer can cause integer overflows, memory     corruption, and       application crashes (bsc#1275096).
    - CVE-2026-56407: integer overflow in doProlog related to entity text length can cause memory corruption     and denial       of service (bsc#1275096).
    - CVE-2026-56408: integer overflow in the copyString function can cause heap memory corruption and     application crashes       (bsc#1275096).
    - CVE-2026-56409: integer overflow in the xmlwf utility output filename handling can allow path buffer     corruption and       arbitrary file write conditions (bsc#1275096).
    - CVE-2026-56410: integer overflow in resolveSystemId within the xmlwf utility can cause memory     corruption, information       disclosure, and potential code execution (bsc#1275096).
    - CVE-2026-56411: integer overflow in endDoctypeDecl via NOTATION declarations in xmlwf can cause memory     corruption and       denial of service (bsc#1275096).
    - CVE-2026-56412: incomplete handler call depth tracking in doCdataSection can cause use-after-free       conditions and arbitrary code execution (bsc#1275096).
    - CVE-2026-66046: libexpat: denial of service vulnerability caused by quadratic algorithmic complexity in     the       storeAtts() function in xmlparse.c (bsc#1275732).
    - CVE-2026-72522: libexpat: out-of-bounds read and resultant infinite loop due to low surrogates being     treated the same       as high surrogates during Unicode processing (bsc#1275594).
    - CVE-2026-76641: Expat through 2.8.3 contains an out-of-bounds read vulnerability that allows attackers     to trigger       memory corruption (bsc#1275915).
    - CVE-2026-76956: 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 X (bsc#1275860).
    - CVE-2026-76957: libexpat before 2.8.4 lacks handler call depth tracking with custom encoding callbacks.
    (bsc#1275859).

    Changes for expat:

    - Updated to version 2.8.4

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

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

The remote openSUSE 16 host has packages installed that are affected by multiple vulnerabilities as referenced in the openSUSE-SU-2026:21945-1 advisory.

    - CVE-2026-41080: crafted XML document can cause a denial of service (bsc#1262263).
    - CVE-2026-45186: 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 (bsc#1264713).
    - CVE-2026-50219: 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     (bsc#1267631).
    - CVE-2026-56131: libexpat before 2.8.2 lacks handler call depth tracking for calls to XML_ResumeParser     from within       handlers in cases of a policy violation (bsc#1268572).
    - CVE-2026-56132: mishandled memory reallocation during array scaffolding in doProlog can cause heap-based     buffer       overflows (bsc#1268573).
    - CVE-2026-56403: integer overflow in the storeAtts function can cause memory corruption and potential     arbitrary code       execution (bsc#1275096).
    - CVE-2026-56404: integer overflow in the addBinding function can cause undersized memory allocations,     memory       corruption, and application crashes (bsc#1275096).
    - CVE-2026-56405: integer overflow in the getAttributeId function can cause heap memory corruption and     arbitrary       code execution (bsc#1275096).
    - CVE-2026-56406: missing bounds validation in XML_ParseBuffer can cause integer overflows, memory     corruption, and       application crashes (bsc#1275096).
    - CVE-2026-56407: integer overflow in doProlog related to entity text length can cause memory corruption     and denial       of service (bsc#1275096).
    - CVE-2026-56408: integer overflow in the copyString function can cause heap memory corruption and     application crashes       (bsc#1275096).
    - CVE-2026-56409: integer overflow in the xmlwf utility output filename handling can allow path buffer     corruption and       arbitrary file write conditions (bsc#1275096).
    - CVE-2026-56410: integer overflow in resolveSystemId within the xmlwf utility can cause memory     corruption, information       disclosure, and potential code execution (bsc#1275096).
    - CVE-2026-56411: integer overflow in endDoctypeDecl via NOTATION declarations in xmlwf can cause memory     corruption and       denial of service (bsc#1275096).
    - CVE-2026-56412: incomplete handler call depth tracking in doCdataSection can cause use-after-free       conditions and arbitrary code execution (bsc#1275096).
    - CVE-2026-66046: libexpat: denial of service vulnerability caused by quadratic algorithmic complexity in     the       storeAtts() function in xmlparse.c (bsc#1275732).
    - CVE-2026-72522: libexpat: out-of-bounds read and resultant infinite loop due to low surrogates being     treated the same       as high surrogates during Unicode processing (bsc#1275594).
    - CVE-2026-76641: Expat through 2.8.3 contains an out-of-bounds read vulnerability that allows attackers     to trigger       memory corruption (bsc#1275915).
    - CVE-2026-76956: 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 X (bsc#1275860).
    - CVE-2026-76957: libexpat before 2.8.4 lacks handler call depth tracking with custom encoding callbacks.
    (bsc#1275859).

    Changes for expat:

    - Updated to version 2.8.4

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

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

The remote Ubuntu 14.04 LTS / 16.04 LTS / 18.04 LTS / 20.04 LTS / 22.04 LTS / 24.04 LTS / 26.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8813-1 advisory.

    It was discovered that Expat did not correctly handle certain integer arithmetic. An attacker could     possibly use this issue to cause a denial of service.

    (CVE-2026-56406, CVE-2026-56407, CVE-2026-56409, CVE-2026-56410, CVE-2026-56411)

    It was discovered that Expat did not correctly track handler call depth. An attacker could possibly use     this issue to cause Expat to crash or execute arbitrary code. (CVE-2026-56131)

    It was discovered that Expat did not correctly handle certain memory operations. An attacker could     possibly use this issue to cause Expat to crash or execute arbitrary code. (CVE-2026-56132)

    It was discovered that Expat did not correctly handle certain Unicode characters. An attacker could     possibly use this issue to cause Expat to use excessive resources, leading to a denial of service.
    (CVE-2026-72522)

    It was discovered that Expat did not correctly process certain XML attributes. A remote attacker could     possibly use this issue to cause Expat to use excessive resources, leading to a denial of service.
    (CVE-2026-66046)

    It was discovered that Expat did not correctly handle certain external entities. An attacker could     possibly use this issue to cause Expat to crash or execute arbitrary code. (CVE-2026-76641)

    It was discovered that Expat did not correctly track handler call depth with custom encodings. An attacker     could possibly use this issue to cause Expat to crash or execute arbitrary code. (CVE-2026-76957)

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

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

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
353452	TencentOS Server 4: expat (TSSA-2026:1058)	Nessus	Tencent Local Security Checks	Local	high
351397	SUSE SLES16 Security Update : expat (SUSE-SU-2026:23912-1)	Nessus	SuSE Local Security Checks	Local	high
350766	openSUSE 16 Security Update : expat (openSUSE-SU-2026:21945-1)	Nessus	SuSE Local Security Checks	Local	high
350173	Ubuntu 14.04 LTS / 16.04 LTS / 18.04 LTS / 20.04 LTS / 22.04 LTS / 24.04 LTS / 26.04 LTS : Expat vulnerabilities (USN-8813-1)	Nessus	Ubuntu Local Security Checks	Local	high
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

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