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Vulnerabilities

Vulnerability · 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 · catalog updated Oct 16, 2026 · Expat before 2.8.5 fails

Check if you run it

No confirmed exploitation is on record for CVE-2026-93990. EPSS is 0.40%. Act only if a listed version of Expat before 2.8.5 fails is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (Expat before 2.8.5 fails).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Unknown—
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.40%
Remediation
Advisory link
Affected products
Debian:12 expat · Debian:13 expat · Debian:14 expat

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

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

How to fix CVE-2026-93990

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-93990. EPSS is 0.40%. Act only if a listed version of Expat before 2.8.5 fails is installed.

Which versions are affected?

Compare what you have installed with 0 → 2.5.0-1+deb12u4, 0 → 2.9.0-1~deb13u1, 0 → 2.8.4-2. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.40%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Technology hubs

Debian security

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Sep 19, 2026 · OpenSSF OSV / OSV Scanner

    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 · OpenSSF OSV / OSV Scanner

    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 · OpenSSF OSV / OSV Scanner

    Fix available

    expat fixed in 2.5.0-1+deb12u4

  4. Oct 16, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    expat fixed in 2.9.0-1~deb13u1

  5. Oct 16, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    expat fixed in 2.8.4-2

  6. Oct 16, 2026 · OpenSSF OSV / OSV Scanner

    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

Sources

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.