CVE-2026-93990
Expat before 2.8.5 Malformed UTF-16 Acceptance via Unchecked Surrogate
CVSS Score
7.5
EPSS Score
0.0%
EPSS Percentile
0th
Expat before 2.8.5 fails to validate that a high surrogate in UTF-16 input is followed by a low surrogate, allowing malformed UTF-16 sequences to be accepted. Attackers can supply UTF-16 encoded XML containing lone high surrogates that consume the following code unit, causing Expat to pass unpaired surrogates to applications built with XML_UNICODE and to silently replace input characters in other builds.
| CWE | CWE-176 |
| Vendor | libexpat |
| Product | libexpat |
| Published | Sep 19, 2026 |
| Last Updated | Sep 28, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None
Affected Versions
libexpat / libexpat
0 < 2.8.5
References
github.com: https://github.com/libexpat/libexpat/pull/1282 github.com: https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861a github.com: https://github.com/libexpat/libexpat/releases/tag/R_2_8_5 blog.hartwork.org: https://blog.hartwork.org/posts/expat-2-8-5-released/ github.com: https://github.com/libexpat/libexpat vulncheck.com: https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogate
Credits
Kartik Kenchi (netliomax25-code)