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libexpat CVE-2026-56411

| EUVDEUVD-2026-38188 MEDIUM
Integer Overflow or Wraparound (CWE-190)
2026-06-21 mitre GHSA-68vw-xv3c-52vp
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

Local vector because xmlwf processes on-disk files; AC:H for required precision in crafting NOTATION count; C:H/I:H reflect heap corruption potential enabling code execution.

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:P/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

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 - 06:43 vuln.today
Analysis Generated
Jun 22, 2026 - 06:43 vuln.today
Patch available
Jun 21, 2026 - 18:01 EUVD

DescriptionCVE.org

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

AnalysisAI

Integer overflow in the xmlwf utility bundled with libexpat before 2.8.2 enables heap corruption via XML documents containing an excessive number of NOTATION declarations in a DOCTYPE block. The flaw in endDoctypeDecl allows a crafted XML file to wrap a signed integer counter, producing an undersized heap allocation that can be overflowed with high confidentiality and integrity impact. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Supply crafted XML with excessive NOTATION declarations
Delivery
xmlwf parses DOCTYPE via endDoctypeDecl callback
Exploit
notationCount signed int wraps at overflow boundary
Execution
undersized NotationList heap buffer allocated
Persist
out-of-bounds write corrupts heap
Impact
arbitrary code execution achieved
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Vulnerability AssessmentAI

Exploitation Exploitation requires that the xmlwf command-line utility (not the libexpat library API itself) be invoked against an attacker-controlled XML document whose DOCTYPE block contains enough NOTATION declarations to overflow a signed 32-bit integer counter - a non-default, edge-case input volume. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 3.1 base score of 6.9 with vector AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L calibrates risk to a local, high-complexity attack scenario where the high C:H and I:H ratings reflect the potential for heap corruption to escalate to code execution. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker crafts an XML file with a DOCTYPE block containing a number of NOTATION declarations sufficient to overflow a signed 32-bit integer and submits it to a CI/CD pipeline, build system, or document processing service that invokes xmlwf for XML validation. The wrapped notationCount causes an undersized heap buffer to be allocated, and the subsequent write of NotationList pointers overflows the buffer, potentially overwriting adjacent heap metadata or function pointers to redirect execution. …
Remediation Upgrade libexpat to version 2.8.2 or later, which reintroduces the notationCount and loop variable as size_t and adds an explicit pre-multiplication overflow guard before the NotationList allocation; the upstream patch is at https://github.com/libexpat/libexpat/pull/1263. … Detailed patch versions, workarounds, and compensating controls in full report.
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Same weakness CWE-190 – Integer Overflow or Wraparound

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Same technique Integer Overflow

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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-2026-56411 vulnerability details – vuln.today
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