GHSA-89v2-g37m-g3ff: 
Python vulnerability analysis and mitigation

The vulnerability (GHSA-89v2-g37m-g3ff) affects the aws-encryption-sdk-cli package and involves improper verification of cryptographic signatures. The issue was discovered and published on May 27, 2021, affecting versions < 1.9.0 and versions >= 2.0.0, < 2.2.0. The vulnerability allows streaming of plaintext from signed messages before ECDSA signature validation is completed (GitHub Advisory).

The vulnerability stems from the ESDK's streaming mode functionality, where the system allows plaintext streaming of signed messages before proper ECDSA signature validation. While the ESDK implements AES-GCM encryption and verifies all plaintext before release, the premature access to plaintext before signature validation poses security concerns. The issue is classified as having moderate severity and is specifically related to CWE-347 (Improper Verification of Cryptographic Signature) (GitHub Advisory).

The vulnerability primarily affects non-repudiation capabilities of the system. While there is no direct impact on the integrity of ciphertext or decrypted plaintext, the flaw could allow an actor with trusted KMS permissions to both decrypt and encrypt messages without proper signature validation. This particularly affects scenarios where applications rely on ECDSA signatures for non-repudiation (GitHub Advisory).

The vulnerability has been patched in versions 1.9.0 and 2.2.0. Users are strongly recommended to upgrade to these versions. For those using streaming features, it's recommended to either ensure client code reads to the end of the stream before using released plaintext or use the new API for streaming with fallback to non-streaming decrypt API for signed messages. Additionally, users processing ESDK messages from untrusted sources should implement the new maximum encrypted data keys parameter (AWS Docs).