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Vulnerability record · CVE-2026-93990 · published 19 September 2026

CVE-2026-93990: Expat through 2.8.4 fails to validate low surrogates following high surrogates in UTF-16 input, allowing malfo…

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.

8.7 CVSS 4.0 High EPSS 0.37% · top 72.1% CWE-176 · CWE-176 Awaiting Analysis
8.7CVSS 4.0 base score
0.37%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
4References
22 Sep 2026Last modified by NVD

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.

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:

References

LinkTags
https://github.com/libexpat/libexpat
https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861a
https://github.com/libexpat/libexpat/pull/1282
https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogate

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Same products first, then exploited flaws of the same weakness class.

7.3CVE-2024-43093Android ExternalStorageProvider path filter bypass via unicode normalizationExternalStorageProvider.java's shouldHideDocument function fails to correctly normalize unicode, allowing a crafted file path to bypass the filter th…KEVEPSS 0.72%analysed

Source: NIST National Vulnerability Database (record CVE-2026-93990), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.