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libexpat CVE-2026-56406

| EUVDEUVD-2026-38183 MEDIUM
Integer Overflow or Wraparound (CWE-190)
2026-06-21 mitre GHSA-v2j6-3q6q-gm3g
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
7.7 HIGH

AV:N reflects libexpat's pervasive use in network services; AC:H retained for integer overflow precision; no auth or interaction required.

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: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 - 06:40 vuln.today
Analysis Generated
Jun 22, 2026 - 06:40 vuln.today
Patch available
Jun 21, 2026 - 17:01 EUVD

DescriptionCVE.org

libexpat before 2.8.2 has an integer overflow in XML_ParseBuffer because it lacked a check that was present in XML_Parse.

AnalysisAI

Integer overflow in libexpat's XML_ParseBuffer function allows potential heap corruption leading to high-confidentiality and high-integrity impact in all libexpat versions before 2.8.2. The overflow occurs because XML_ParseBuffer lacked a bounds check on the byte index accumulator that was already present in the sibling XML_Parse function - a defensive guard omitted asymmetrically between two code paths. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Supply crafted XML stream to target application
Delivery
Application calls XML_ParseBuffer incrementally
Exploit
Accumulate len values to overflow m_parseEndByteIndex
Execution
Corrupt internal parser offset state
Persist
Achieve heap write primitive
Impact
Execute arbitrary code in application context
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Vulnerability AssessmentAI

Exploitation The vulnerable code path is only reachable when an application explicitly calls XML_ParseBuffer rather than XML_Parse - a developer choice that is common in streaming and zero-copy parsing patterns but not universal. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The provided CVSS 3.1 vector (AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L) scores 6.9 and assigns a local attack vector with high complexity. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker controls XML content processed by an application using XML_ParseBuffer in incremental mode - for example, a document editor, a messaging daemon, or a network service consuming XML-encoded data. By crafting a sequence of buffer chunks whose cumulative byte lengths cause m_parseEndByteIndex to overflow XML_INDEX_MAX, the attacker corrupts internal parser state. …
Remediation Upgrade libexpat to version 2.8.2 or later, which introduces the overflow guard in XML_ParseBuffer mirroring the check already in XML_Parse. … Detailed patch versions, workarounds, and compensating controls in full report.
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Same weakness CWE-190 – Integer Overflow or Wraparound

View all
CVE-2013-2729 CRITICAL POC
9.8
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CVE-2012-5054 HIGH POC
8.8
CVE-2014-0569 CRITICAL POC
9.3
CVE-2017-3599 HIGH POC
7.5
CVE-2017-7529 HIGH
7.5
CVE-2016-1010 HIGH
8.8
CVE-2013-3940 CRITICAL
9.3

Same technique Integer Overflow

View all
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-2017-3599 HIGH POC
7.5
CVE-2017-7529 HIGH
7.5
CVE-2016-1010 HIGH
8.8

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-2026-56406 vulnerability details – vuln.today
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