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libexpat CVE-2026-56408

| EUVDEUVD-2026-38185 MEDIUM
Integer Overflow or Wraparound (CWE-190)
2026-06-21 mitre GHSA-9jq5-63hm-6q5g
Integer Overflow Buffer Overflow Libexpat Suse
6.9
CVSS 3.1 · Vendor: mitre
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Severity by source

Vendor (mitre) PRIMARY
6.9 MEDIUM
AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L
vuln.today AI
7.7 HIGH

AV:N because libexpat typically processes untrusted network-sourced XML; AC:H because reliable heap overflow exploitation requires precise heap layout control.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L
4.0 AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N
SUSE
MEDIUM
qualitative

Primary rating from Vendor (mitre).

CVSS VectorVendor: mitre

CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L
Attack Vector
Local
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
Low

Lifecycle Timeline

3
Source Code Evidence Fetched
Jun 22, 2026 - 06:42 vuln.today
Analysis Generated
Jun 22, 2026 - 06:42 vuln.today
Patch available
Jun 21, 2026 - 17:01 EUVD

DescriptionCVE.org

libexpat before 2.8.2 has an integer overflow in copyString.

AnalysisAI

Integer overflow in libexpat's copyString function (xmlparse.c) allows heap buffer overflow when processing specially crafted XML input, affecting all libexpat versions before 2.8.2. The missing bounds check on a size multiplication permits an attacker-controlled string length to wrap around SIZE_MAX, producing an undersized heap allocation that is subsequently overwritten - enabling potential memory corruption, arbitrary code execution, or data disclosure in any application consuming the library. No public exploit has been identified at time of analysis; a vendor-released patch is available in libexpat 2.8.2.

Technical ContextAI

libexpat (cpe:2.3:a:libexpat_project:libexpat:*:*:*:*:*:*:*:*) is a widely deployed C library for stream-oriented XML parsing, used transitively by Python, PHP, Apache httpd, and numerous Linux distribution packages. The defective code path is the copyString function in expat/lib/xmlparse.c. The root cause is CWE-190 (Integer Overflow or Wraparound): before the fix, charsRequired was multiplied by sizeof(XML_Char) without first checking whether the product would exceed SIZE_MAX. Commit 16e2efd867ea8567ffa012210b52ef5918e20817 adds the guard 'if (charsRequired > SIZE_MAX / sizeof(XML_Char)) return NULL;' directly before the allocation. Without that guard, a sufficiently large charsRequired value causes the product to wrap to a small number, malloc allocates a tiny buffer, and the subsequent string copy writes far beyond its bounds - a classic integer-overflow-to-heap-buffer-overflow pattern.

RemediationAI

The primary fix is to upgrade libexpat to version 2.8.2 or later, which incorporates the integer overflow guard added in upstream commit 16e2efd867ea8567ffa012210b52ef5918e20817 (https://github.com/libexpat/libexpat/commit/16e2efd867ea8567ffa012210b52ef5918e20817). System administrators should update distribution-provided libexpat packages (e.g., apt upgrade libexpat1, dnf upgrade expat) and rebuild any statically linked applications against the patched library. Where immediate patching is not feasible, restrict which sources can supply XML to affected applications - for example, by rejecting XML input from untrusted network origins at a WAF or API gateway layer and enforcing strict maximum payload sizes. Note that size-limit controls reduce the attack surface but are not a complete mitigation, as the triggering string length may fall within commonly accepted bounds depending on the application context.

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Same weakness CWE-190 – Integer Overflow or Wraparound

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CVE-2013-2729 CRITICAL POC
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CVE-2014-0569 CRITICAL POC
9.3
CVE-2023-21716 CRITICAL POC
9.8
CVE-2017-3599 HIGH POC
7.5
CVE-2017-7529 HIGH
7.5
CVE-2016-1010 HIGH
8.8

Same technique Integer Overflow

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CVE-2014-0497 CRITICAL POC
9.8
CVE-2013-2729 CRITICAL POC
9.8
CVE-2015-8651 HIGH
8.8
CVE-2012-5054 HIGH POC
8.8
CVE-2014-0569 CRITICAL POC
9.3
CVE-2023-21716 CRITICAL POC
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CVE-2017-3599 HIGH POC
7.5
CVE-2017-7529 HIGH
7.5

Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SLES15-SP5-CHOST-BYOS-SAP-CCloud Not-Affected
SLES15-SP5-CHOST-BYOS-SAP-CCloud Affected
SLES15-SP6-CHOST-BYOS Affected
SLES15-SP6-CHOST-BYOS-Aliyun Affected
SLES15-SP6-CHOST-BYOS-Azure Affected

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CVE-2026-56408 vulnerability details – vuln.today
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