CVE-2026-93990 (CVSS 7.5)

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.

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CVSS v3.1 Score

7.5

HIGH

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

EPSS — Exploit Prediction

0.0040

Probability of exploitation

0.32%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-176 CWE-176

References

Other References

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

Frequently Asked Questions

What is CVE-2026-93990? +

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. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-93990? +

CVE-2026-93990 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0040, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-93990? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2026-93990