CVE-2026-93990

Summary

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.

Affected Software

Weaknesses

• CWE-176: Improper Handling of Unicode Encoding

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: yes
  • Technical Impact: partial

References

• https://github.com/libexpat/libexpat/pull/1282
• https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861a
• https://github.com/libexpat/libexpat/releases/tag/R_2_8_5
• https://blog.hartwork.org/posts/expat-2-8-5-released/
• https://github.com/libexpat/libexpat
• https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogate

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