CVE-2026-6550 is a cryptographic vulnerability classified under CWE-757 (Selection of Less-Secure Algorithm During Negotiation) in the AWS Encryption SDK for Python. The issue allows an authenticated local attacker to downgrade the cryptographic algorithm used in the caching layer, bypassing key commitment policy enforcement. This can cause ciphertext to decrypt to multiple different plaintexts, undermining data integrity. The vulnerability affects versions prior to 3.3.1 and 4.0.5. AWS has released patched versions 3.3.1 and 4.0.5 to remediate the issue. The vulnerability has a CVSS v3.1 score of 4.7 (medium severity) with attack vector local, high attack complexity, low privileges required, no user interaction, unchanged scope, no confidentiality impact, high integrity impact, and no availability impact. AWS manages remediation for this cloud-hosted service, and users should upgrade to the fixed versions.

An authenticated local attacker can exploit this vulnerability to downgrade the cryptographic algorithm used in the caching layer of the AWS Encryption SDK for Python. This bypasses key commitment policy enforcement, potentially allowing ciphertext to decrypt to multiple different plaintexts. This impacts data integrity but does not affect confidentiality or availability. The vulnerability does not appear to be exploited in the wild at this time.

AWS has released fixed versions 3.3.1 and 4.0.5 of the AWS Encryption SDK for Python that address this vulnerability. Users should upgrade to these versions to remediate the issue. Since this is a cloud service, AWS manages remediation server-side, but users running local instances or SDK integrations should apply the update. Patch status is confirmed by the vendor advisory at https://aws.amazon.com/security/security-bulletins/2026-017-aws/.