Heap overflow via unchecked output-path size arithmetic
Published Jun 21, 2026 · Updated Jun 21, 2026
Integer overflow in Expat libexpat's xmlwf before 2.8.2 allows local users to corrupt heap memory through crafted output paths. In main's -d branch, unchecked additions and multiplication size the joined outputDir and input filename before tcscpy and tcscat copy them into an underallocated buffer. The attack requires user interaction and path components long enough to wrap the size calculation; the resulting heap overflow corrupts process memory.
Summary
What happened
Integer overflow in Expat libexpat's xmlwf before 2.8.2 allows local users to corrupt heap memory through crafted output paths. In main's -d branch, unchecked additions and multiplication size the joined outputDir and input filename before tcscpy and tcscat copy them into an underallocated buffer. The attack requires user interaction and path components long enough to wrap the size calculation; the resulting heap overflow corrupts process memory.
The record
- CVE
- CVE-2026-56409
- Published
- Jun 21, 2026
- Updated
- Jun 21, 2026
- Vendor
- Expat Project
- Product
- libexpat
- Classifications
- CWE-190, T1203
- 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?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <2.8.2
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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