CVE-2025-0239 — When using Alt-Svc, ALPN did not properly validate certificates when the original server is redirecting to an insecure site

Matched remediation archetype

Cryptography, certificate, signature, and channel validation

This catalog composition supplies bounded fallback guidance. Explicitly reviewed curated workflows load with the complete record below.

Check exposure

• Inventory affected algorithms, key uses, trust stores, certificate validation settings, random sources, and plaintext channels across clients and services.
• Determine which secrets, identities, signatures, or data protections depend on the affected primitive or validation path.
• Check debug, compatibility, fallback, and hostname or audience override settings in build and runtime configuration.

Remediate safely

• Use a maintained platform cryptographic API with approved algorithms, modes, parameters, randomness, and full peer identity validation.
• Remove insecure fallback and validation bypasses; separate keys by purpose and load them from managed secret storage.
• Plan rotation or reissuance for affected keys, certificates, tokens, hashes, or ciphertext and document compatibility sequencing.