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Findings

CVE-2026-93990

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.

Published Sep 19, 2026 · updated Oct 16, 2026

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.

Code

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No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Sep 19, 2026 · OSV.dev

    Detected

    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

  2. Oct 16, 2026 · OSV.dev

    Fix available

    expat fixed in 2.5.0-1+deb12u4; expat fixed in 2.9.0-1~deb13u1; expat fixed in 2.8.4-2

  3. Oct 16, 2026 · OSV.dev

    Fix available

    expat fixed in 2.5.0-1+deb12u4

  4. Oct 16, 2026 · OSV.dev

    Fix available

    expat fixed in 2.9.0-1~deb13u1

  5. Oct 16, 2026 · OSV.dev

    Fix available

    expat fixed in 2.8.4-2

  6. Oct 16, 2026 · OSV.dev

    Updated

    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

Affected

  • Debian:12 expat0 → 2.5.0-1+deb12u4
  • Debian:13 expat0 → 2.9.0-1~deb13u1
  • Debian:14 expat0 → 2.8.4-2

Sources

References