Memory corruption via unchecked copyString allocation
Published Jun 21, 2026 · Updated Jun 21, 2026
Integer overflow in copyString in Expat Project libexpat before 2.8.2 allows local users to corrupt parser memory during XML processing. The function measures an XML_Char string and its terminator, then multiplies that count by sizeof(XML_Char) for allocation without first bounding the multiplication; wrapping produces an undersized buffer for the copy. Reaching the overwrite requires a build where XML_Char is wider than one byte and an enormous string reaching copyString; the public record does not identify which parser input supplies that string.
Summary
What happened
Integer overflow in copyString in Expat Project libexpat before 2.8.2 allows local users to corrupt parser memory during XML processing. The function measures an XML_Char string and its terminator, then multiplies that count by sizeof(XML_Char) for allocation without first bounding the multiplication; wrapping produces an undersized buffer for the copy. Reaching the overwrite requires a build where XML_Char is wider than one byte and an enormous string reaching copyString; the public record does not identify which parser input supplies that string.
The record
- CVE
- CVE-2026-56408
- 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?
Published CVSS scores
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Attacks
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Public exploit references
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Technologies
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Your stack
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