{"id":"CVE-2026-93990","title":"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","summary":"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 c…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","cwe":["CWE-176","CWE-91"],"vendor":"libexpat","product":"libexpat","affected":["libexpat <= 2.8.4"],"patched":["hardened_images"],"published":"2026-09-19","updated":"2026-09-28","sourceUpdated":"2026-09-28T17:17:53.037","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-93990","references":[{"url":"https://blog.hartwork.org/posts/expat-2-8-5-released/","label":"disclosure@vulncheck.com"},{"url":"https://github.com/libexpat/libexpat","label":"disclosure@vulncheck.com"},{"url":"https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861a","label":"disclosure@vulncheck.com"},{"url":"https://github.com/libexpat/libexpat/pull/1282","label":"disclosure@vulncheck.com"},{"url":"https://github.com/libexpat/libexpat/releases/tag/R_2_8_5","label":"disclosure@vulncheck.com"},{"url":"https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogate","label":"disclosure@vulncheck.com"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-93990.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-93990"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2538967"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-93990"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-93990"},{"url":"https://access.redhat.com/errata/RHSA-2026:71655"},{"url":"https://access.redhat.com/errata/RHSA-2026:74001"},{"url":"https://access.redhat.com/errata/RHSA-2026:72663"},{"url":"https://access.redhat.com/errata/RHSA-2026:72448"},{"url":"https://access.redhat.com/errata/RHSA-2026:79357"}],"tags":["nvd","cve.org","csaf","vex","red-hat"],"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"partial","timestamp":"2026-09-21T15:10:43.564847Z"},"ingestedAt":"2026-09-19T23:10:34.247Z","epss":0.00403,"epssPercentile":0.34409,"slug":"CVE-2026-93990","body":"## Overview\n\nExpat 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · Important · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, … · updated 2026-10-09 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-93990.json)\n- **RHSA-2026:71655** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-24 · [advisory](https://access.redhat.com/errata/RHSA-2026:71655)\n- **RHSA-2026:74001** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 10), Red Hat Enterprise Linux BaseOS (v. 10) · released 2026-09-30 · [advisory](https://access.redhat.com/errata/RHSA-2026:74001)\n- **RHSA-2026:72663** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 9), Red Hat Enterprise Linux BaseOS (v. 9) · released 2026-09-29 · [advisory](https://access.redhat.com/errata/RHSA-2026:72663)\n- **RHSA-2026:72448** · Red Hat · fixed in: Red Hat Enterprise Linux BaseOS (v. 8) · released 2026-09-28 · [advisory](https://access.redhat.com/errata/RHSA-2026:72448)\n- **RHSA-2026:79357** · Red Hat · fixed in: Red Hat Cost Management On-Premise 1 · released 2026-10-08 · [advisory](https://access.redhat.com/errata/RHSA-2026:79357)","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}