Name: CVE-2026-93990: Improper Handling of Unicode Encoding
Creator: Rapid7
Published: 2026-09-19T00:00:00.000Z
License: https://www.rapid7.com/legal/website-terms-of-use/
Keywords: CVE, CVE-2026-93990, CWE-176, CVSS 7.5, EPSS 0.00403

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 Details

CVSS 4.0 Base Score: 8.7 (HIGH)
CVSS 4.0 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/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)
CVSS 3.1 Base Score: 7.5
CVSS 3.1 Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N)

Covered by Rapid7

Product	Vendor Advisory	Solution File	Added	Published
Alma_linux	—	Upgrade expatUpgrade expat-devel	Oct 11, 2026	Sep 28, 2026
Alpine Linux	—	Upgrade expat	Sep 24, 2026	Sep 19, 2026
Amazon_linux_2023	—	Upgrade firefoxUpgrade firefox-debuginfoUpgrade firefox-debugsource	Oct 13, 2026	Sep 19, 2026
Debian	—	Upgrade expat	Oct 5, 2026	Sep 19, 2026
Freebsd	—	Upgrade expat	Oct 5, 2026	Oct 4, 2026
Redhat_linux	—	Upgrade expat-debuginfoUpgrade expat-develNo solution existsUpgrade expat-debugsourceUpgrade expat	Sep 28, 2026	Sep 19, 2026
Rocky_linux	—	Upgrade expat-debuginfoUpgrade expat-debugsourceUpgrade expatUpgrade expat-devel	Sep 30, 2026	Sep 29, 2026

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CVSS Details

Covered by Rapid7

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