CVE-2026-63687: Apache CXF: JwtRequestCodeFilter silently overrides outer PKCE and nonce parameters

Severity: critical (CVSS 9.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-06 · updated 2026-10-24
Weakness: CWE-345

Description

Apache CXF's JwtRequestCodeFilter copies all claims from a signed request JWT into the authorization parameter map without excluding security-sensitive parameters. A client that can produce a validly-signed request JWT (e.g., one whose client_secret is known or compromised) can thereby substitute the code_challenge, code_challenge_method, nonce, and state values that were set in the outer HTTP request, undermining PKCE integrity and OpenID Connect replay protection. Users are recommended to upgrade to versions 4.2.3 or 4.1.8 or 3.6.12, which fix this issue.

Affected products

Apache Software Foundation Apache CXF: before 3.6.12; from 4.0.0 before 4.1.8; from 4.2.0 before 4.2.3 — fixed in 3.6.12, 4.1.8, 4.2.3

How to fix

Upgrade to a fixed version: Apache Software Foundation Apache CXF 3.6.12, 4.1.8, 4.2.3. Check the vendor advisory for mitigations.

References

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