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libexpat xmlwf CVE-2026-56410

| EUVDEUVD-2026-38187 MEDIUM
Integer Overflow or Wraparound (CWE-190)
2026-06-21 mitre GHSA-638v-9w3r-gh6q
Integer Overflow Buffer Overflow Libexpat Red Hat 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
6.9 MEDIUM

AV:L because xmlwf requires local execution; AC:H because triggering size_t overflow demands impractically large combined string lengths, especially on 64-bit; C:H/I:H for heap corruption enabling code execution; A:L for incidental crash potential.

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

Primary rating from Vendor (mitre).

CVSS VectorVendor: mitre

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

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

AnalysisAI

Integer overflow in libexpat's xmlwf tool allows an attacker supplying a crafted XML file with an excessively long DOCTYPE system identifier to trigger a heap buffer overflow via the resolveSystemId function. All libexpat versions before 2.8.2 are affected; the root cause is an unchecked size_t arithmetic operation - both the addition of string lengths and the subsequent multiplication by sizeof(XML_Char) - before a malloc call. No public exploit has been identified at time of analysis, and exploitation requires local access under high-complexity conditions per the CVSS:3.1/AV:L/AC:H vector.

Technical ContextAI

libexpat (CPE: cpe:2.3:a:libexpat_project:libexpat:*:*:*:*:*:*:*:*) is a widely embedded C XML parsing library. The xmlwf command-line tool, bundled with libexpat, checks XML documents for well-formedness. The vulnerable function resolveSystemId in expat/xmlwf/xmlfile.c computes a malloc size as (tcslen(base) + tcslen(systemId) + 2) * sizeof(XML_Char) - a two-stage arithmetic operation susceptible to CWE-190 Integer Overflow. Stage one: the addition of the two string lengths plus 2 can wrap around the size_t maximum without error. Stage two: multiplying the (already potentially wrapped) result by sizeof(XML_Char) can independently overflow. Either overflow produces a malloc argument far smaller than the actual required buffer, resulting in a subsequent heap write beyond the allocated region. The fix in PR #1252 introduces explicit bounds checks using SIZE_MAX arithmetic before both the addition and multiplication, returning the raw systemId pointer as a safe fallback when overflow would occur.

RemediationAI

Upgrade libexpat to version 2.8.2 or later, which incorporates the integer-overflow guards added in PR #1252. Downstream Linux distributions and BSDs that package libexpat should be monitored for updated packages. The vendor advisory is referenced at https://nvd.nist.gov/vuln/detail/CVE-2026-56410 and the VulDB entry at https://vuldb.com/vuln/372645. Where an immediate upgrade is not feasible, restrict or eliminate the use of the xmlwf command-line tool on untrusted input, noting that this mitigation does not protect other applications that may bundle libexpat source internally. If xmlwf is used in automated pipelines, add input validation to reject XML files with abnormally long DOCTYPE system identifier strings as a compensating control - this reduces the attack surface but is not a substitute for patching. The core libexpat parsing engine is unaffected by this specific integer overflow; only environments invoking xmlwf need emergency mitigation.

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Same weakness CWE-190 – Integer Overflow or Wraparound

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Same technique Integer Overflow

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CVE-2014-0497 CRITICAL POC
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CVE-2015-8651 HIGH
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CVE-2012-5054 HIGH POC
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CVE-2014-0569 CRITICAL POC
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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-2026-56410 vulnerability details – vuln.today
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