Answer in brief
CVE-2026-93990 records a High severity (CVSS 8.7) vulnerability in Expat before 2.8.5 Malformed UTF-16 Acceptance via Unchecked Surrogate. The current sources do not mark it as known exploited. The current feed maps libexpat/libexpat (generic), libexpat/libexpat (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 8.7. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps libexpat/libexpat (generic), libexpat/libexpat (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| libexpat/libexpatgeneric | 0 | Not reported |
| libexpat/libexpatgeneric | >=0 <2.8.5 | 2.8.5 |
Published upstream
Sep 19, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 28, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Sep 19, 2026
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.
Quoted source text, attributed separately from HOL analysis.