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web-token/jwt-experimental: Chacha20Poly1305 AEAD downgrade to unauthenticated ChaCha20

The experimental Chacha20Poly1305 key-encryption algorithm discards the Poly1305 authentication tag during encryption and does not verify it during decryption, degrading AEAD to unauthenticated ChaCha20.

19 Jun 2026Read 1 minSeverity: act now

What changed

The experimental Chacha20Poly1305 key-encryption algorithm discards the Poly1305 authentication tag during encryption and does not verify it during decryption, degrading AEAD to unauthenticated ChaCha20. The fix publishes the tag as a 'tag' header parameter and verifies it.

Who it affects

Applications that register Jose\Experimental\KeyEncryption\Chacha20Poly1305 as a JWE 'alg' algorithm.

What to do today

Upgrade to the patched version immediately and do not use the experimental Chacha20Poly1305 algorithm for untrusted input until upgraded.

The trail
Collected Audited Written Published