CVE-2026-93990Expat before 2.8.5 Malformed UTF-16 Acceptance via Unchecked Surrogate
Updated under an hour ago ()
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It affects libexpat. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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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.
- CVSS
- 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- Weakness (CWE)
- CWE-176
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- VulnCheck
- NVD analysis
- Awaiting Analysis
- Record last updated
- Sep 28, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
libexpat libexpat libexpat:libexpat (from the name) | before 2.8.5; 2.8.5 not affected | CNA record |
References
- https://github.com/libexpat/libexpat/pull/1282issue-tracking, patch
- 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
- https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogatethird-party-advisory
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.