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Findings

CVE-2026-66046

Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified at

Published Aug 18, 2026 · updated Oct 16, 2026

Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified attributes with non-normalized values triggers an O(N^2) linear scan of elementType->defaultAtts to determine CDATA status. A remote unauthenticated attacker can supply a single well-formed XML document of a few megabytes to an application parsing untrusted XML to cause excessive CPU consumption, resulting in denial of service without requiring authentication, external entity resolution, or non-default parser options.

Code

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No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Aug 18, 2026 · OSV.dev

    Detected

    Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified attributes with non-normalized values triggers an O(N^2) linear scan of elementType->defaultAtts to determine CDATA status. A remote unauthenticated attacker can supply a single well-formed XML document of a few megabytes

  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 2.8.4-1

  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 2.8.4-1

  6. Oct 16, 2026 · OSV.dev

    Updated

    Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified attributes with non-normalized values triggers an O(N^2) linear scan of elementType->defaultAtts to determine CDATA status. A remote unauthenticated attacker can supply a single well-formed XML document of a few megabytes

Affected

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

Sources

References