Expat before 2.8.5 Malformed UTF-16 Acceptance via Unchecked Surrogate (libexpat libexpat)
At a glance
- Source
- NVD
- EPSS
- EPSS 0.40 % · percentile 35 ()
- State
- PUBLISHED
- Published
- Updated
- Assigner
- VulnCheck
- NVD status
- Awaiting Analysis
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.
Weaknesses (CWE)
- CWE-176 — Improper Handling of Unicode Encoding
References
- https://github.com/libexpat/libexpat/pull/1282
- https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861a
- https://github.com/libexpat/libexpat/releases/tag/R_2_8_5
- https://blog.hartwork.org/posts/expat-2-8-5-released/
- https://github.com/libexpat/libexpat
- https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogate
Scores
| Version | Score | Vector | Scored by |
|---|---|---|---|
| CVSS 4.0 | HIGH 8.7 | 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 |
| CVSS 3.1 | HIGH 7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N | VulnCheck |
| CVSS 4.0 | HIGH 8.7 | 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X | NVD · disclosure@vulncheck.com (Secondary) |
| CVSS 3.1 | HIGH 7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N | NVD · disclosure@vulncheck.com (Secondary) |
European references
- ENISA EUVD · EUVD-2026-83618
- GCVE · GCVE-0-2026-93990
CERT-FR advisories
- CERTFR-2026-AVI-1431 — Multiples vulnérabilités dans le noyau Linux de Red Hat · cert.ssi.gouv.fr
- CERTFR-2026-AVI-1390 — Multiples vulnérabilités dans Tenable Network Monitor · cert.ssi.gouv.fr
- CERTFR-2026-AVI-1385 — Multiples vulnérabilités dans les produits VMware · cert.ssi.gouv.fr
Affected products
| Product | Versions |
|---|---|
| libexpat · libexpat | affected 0 < 2.8.5 ; unaffected 2.8.5 |
Sources
| Source | Licence |
|---|---|
| CVE List (CVEProject cvelistV5) | CVE Program Terms of Use |
| EPSS (FIRST.org) | FIRST — attribution requested |
| ENISA EUVD | ENISA — reproduction authorised, source acknowledged |
| CERT-FR (ANSSI) | Licence Ouverte / Etalab 2.0 |
| NVD (NIST) via fkie-cad/nvd-json-data-feeds | Public domain — this product uses data from the NVD API but is not endorsed or certified by the NVD |