Description
Expat through 2.8.4 fails to validate low surrogates following high surrogates in UTF-16 input, allowing malformed UTF-16 sequences to be accepted. Attackers can craft UTF-16 encoded XML with lone high surrogates that consume following code units, hiding markup characters from the parser and enabling XML injection attacks.
Published: 2026-09-19
Score: 8.7 High
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

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History

Sat, 19 Sep 2026 23:00:00 +0000

Type Values Removed Values Added
Description Expat through 2.8.4 fails to validate low surrogates following high surrogates in UTF-16 input, allowing malformed UTF-16 sequences to be accepted. Attackers can craft UTF-16 encoded XML with lone high surrogates that consume following code units, hiding markup characters from the parser and enabling XML injection attacks.
Title Expat through 2.8.4 Malformed UTF-16 Acceptance via Unchecked Surrogate
First Time appeared Libexpat Project
Libexpat Project libexpat
Weaknesses CWE-176
CPEs cpe:2.3:a:libexpat_project:libexpat:*:*:*:*:*:*:*:*
Vendors & Products Libexpat Project
Libexpat Project libexpat
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N'}

cvssV4_0

{'score': 8.7, 'vector': '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'}

Subscriptions

Libexpat Project Libexpat
cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-09-19T22:58:11.224Z

Reserved: 2026-09-19T10:55:49.093Z

Link: CVE-2026-93990

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-19T23:17:10.203

Modified: 2026-09-19T23:17:10.203

Link: CVE-2026-93990

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses
  • CWE-176

    Improper Handling of Unicode Encoding