CVE-2026-93990
Expat before 2.8.5 Malformed UTF-16 Acceptance via Unchecked Surrogate
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.
Fixes and workarounds
Fix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: CNA: VulnCheckFix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: CNA: VulnCheckAffected products and versions
| Product | Versions | Authority |
|---|---|---|
| libexpat libexpat libexpat/libexpat
github |
≥ 0; < 2.8.5 (affected, semver) 2.8.5 (unaffected, semver) Other versions: unaffected |
CNA: VulnCheck |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 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 | CNA: 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 | CNA: VulnCheck |
Exploit evidence
No exploit evidence in collected sources. This is not proof of no exploitation.
References
- https://github.com/libexpat/libexpat/pull/1282CNA: VulnCheck · issue-tracking, patch
- https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861aCNA: VulnCheck · patch
- https://github.com/libexpat/libexpat/releases/tag/R_2_8_5CNA: VulnCheck · release-notes
- https://blog.hartwork.org/posts/expat-2-8-5-released/CNA: VulnCheck · vendor-advisory
- https://github.com/libexpat/libexpatCNA: VulnCheck · product
- https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogateCNA: VulnCheck · third-party-advisory
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