CVE-2026-93990
Expat before 2.8.5 Malformed UTF-16 Acceptance via Unchecked Surrogate
- State
- Published
- Severity
- 8.7 High
- Published
- Sep 19, 2026
- Updated
- Sep 28, 2026
- Reserved
- Sep 19, 2026
Description
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 8.7 High | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N | VulnCheck |
| 3.1 | 7.5 High | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N | VulnCheck |
Weaknesses
- CWE-176 Improper Handling of Unicode Encoding
Affected Products
| Product | Versions |
|---|---|
libexpatlibexpat |
|
References
- GitHub PR #1282issue-trackingpatch
- https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861apatch
- https://github.com/libexpat/libexpat/releases/tag/R_2_8_5release-notes
- https://blog.hartwork.org/posts/expat-2-8-5-released/vendor-advisory
- https://github.com/libexpat/libexpatproduct
- VulnCheck Advisory: Expat through 2.8.4 Malformed UTF-16 Acceptance via Unchecked Surrogatethird-party-advisory
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