CVE-2026-93990
Expat through 2.8.4 Malformed UTF-16 Acceptance via Unchecked Surrogate
CVSS Score
7.5
EPSS Score
0.0%
EPSS Percentile
0th
Expat through 2.8.4 fails to validate low surrogates following high surrogates in UTF-16 input, allowing malformed UTF-16 sequences to be accepted. Attackers can craft UTF-16 encoded XML with lone high surrogates that consume following code units, hiding markup characters from the parser and enabling XML injection attacks.
| CWE | CWE-176 |
| Vendor | libexpat |
| Product | libexpat |
| Published | Sep 19, 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 ≤ 2.8.4
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 vulncheck.com: https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogate
Credits
Kartik Kenchi (netliomax25-code)