CVE-2026-93990

high

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.

References

https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogate

https://github.com/libexpat/libexpat/releases/tag/R_2_8_5

https://github.com/libexpat/libexpat/pull/1282

https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861a

https://github.com/libexpat/libexpat

https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-83618

https://blog.hartwork.org/posts/expat-2-8-5-released/

Details

Source: Mitre, NVD

Published: 2026-09-19

Updated: 2026-09-28

Risk Information

CVSS v2

Base Score: 7.8

Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:C/A:N

Severity: High

CVSS v3

Base Score: 7.5

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Severity: High

CVSS v4

Base 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

Severity: High

EPSS

EPSS: 0.00403