Local code execution via namespace URI overflow
Published Jun 21, 2026 · Updated Jun 21, 2026
Integer overflow in libexpat before 2.8.2 allows local users to execute arbitrary code through crafted XML namespace URIs. The addBinding function uses a signed int to count a NUL-terminated namespace URI and to add a namespace separator without first guarding INT_MAX. Exploitation requires local access, high complexity, and an application that parses attacker-controlled XML; successful exploitation runs code in that application's context.
Summary
What happened
Integer overflow in libexpat before 2.8.2 allows local users to execute arbitrary code through crafted XML namespace URIs. The addBinding function uses a signed int to count a NUL-terminated namespace URI and to add a namespace separator without first guarding INT_MAX. Exploitation requires local access, high complexity, and an application that parses attacker-controlled XML; successful exploitation runs code in that application's context.
The record
- CVE
- CVE-2026-56404
- Published
- Jun 21, 2026
- Updated
- Jun 21, 2026
- Vendor
- Expat Project
- Product
- libexpat
- Classifications
- CWE-190
- Attack vector
- local
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 21, 2026CVE publishedPublication date reported by the CVE source.
- Jun 21, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=0 <2.8.2
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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