Memory corruption via overflowed notation-list allocation
Published Jun 21, 2026 · Updated Jun 21, 2026
Integer overflow in xmlwf in Expat Project libexpat before 2.8.2 allows local users to corrupt memory via crafted NOTATION declarations. endDoctypeDecl counts DTD NOTATION entries in a signed int, multiplies the count by the pointer size without an overflow guard, under-allocates the notation list, and then writes every entry. The overflow requires a 32-bit build and enough declarations to wrap the allocation-size calculation; resulting out-of-bounds writes corrupt xmlwf process memory.
Summary
What happened
Integer overflow in xmlwf in Expat Project libexpat before 2.8.2 allows local users to corrupt memory via crafted NOTATION declarations. endDoctypeDecl counts DTD NOTATION entries in a signed int, multiplies the count by the pointer size without an overflow guard, under-allocates the notation list, and then writes every entry. The overflow requires a 32-bit build and enough declarations to wrap the allocation-size calculation; resulting out-of-bounds writes corrupt xmlwf process memory.
The record
- CVE
- CVE-2026-56411
- 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
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Is a vulnerable build present?
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- Affected versionversion=0 <2.8.2
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