GHSA-h45p-w933-jxh3: 
JavaScript vulnerability analysis and mitigation

The vulnerability (GHSA-h45p-w933-jxh3) affects the aws-encryption-sdk-javascript package and involves improper verification of cryptographic signatures. The issue was discovered and published on May 27, 2021, affecting versions < 1.9.0 and >= 2.0.0, < 2.2.0 of both @aws-crypto/client-browser and @aws-crypto/client-node packages. The vulnerability is classified as moderate severity and primarily concerns the streaming mode functionality where plaintext of signed messages could be processed before ECDSA signature validation (GitHub Advisory).

The vulnerability stems from the ESDK's streaming mode implementation where callers could stream the plaintext of signed messages before the ECDSA signature validation was completed. While the system uses AES-GCM encryption and verifies all plaintext before release, the premature access to plaintext before signature validation could compromise non-repudiation guarantees. Additionally, the vulnerability allowed actors with trusted KMS permissions to decrypt messages to potentially encrypt messages without proper signature validation (GitHub Advisory).

The vulnerability's impact is primarily focused on scenarios where applications rely on ECDSA signatures for non-repudiation. While there is no direct impact on the integrity of the ciphertext or decrypted plaintext, the issue could allow actors with KMS permissions to bypass signature validation controls. The vulnerability also exposed systems to potential processing of messages with excessive Encrypted Data Keys (EDKs), which could lead to unnecessary AWS KMS Decrypt API calls (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, the patch introduces a new API specifically for streaming unsigned messages, with a fallback to non-streaming decrypt API for signed messages. Additionally, a new configuration parameter has been introduced to limit the number of Encrypted Data Keys (EDKs) that the ESDK will process per message, helping protect against potential abuse. Users processing ESDK messages from untrusted sources should implement the new maximum encrypted data keys parameter (GitHub Advisory).