Ciphertext integrity bypass via unchecked cached materials

Cryptographic downgrade in affected AWS Encryption SDK for Python releases allows local users to undermine ciphertext integrity via a shared cache. The caching materials manager reuses encryption materials created under a weaker client's policy without checking their algorithm suite against the requesting client's commitment policy. Exploitation requires two same-process clients with different policies to share one cache, the weaker client to warm it first, matching encryption contexts, default algorithm suites, and attacker-controlled ciphertext; a recipient can then decrypt a message different from the one encrypted.