Vulnerability · Published Apr 20, 2026 · Assigned by AMZN
CVE-2026-6550Key commitment policy bypass via shared key cache in AWS Encryption SDK for Python
Medium 4.7
In plain English
A medium-severity security flaw in AWS Encryption SDK for Python from AWS. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 1% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Cryptographic algorithm downgrade in the caching layer of Amazon AWS Encryption SDK for Python before version 3.3.1 and before version 4.0.5 might allow an authenticated local threat actor to bypass key commitment policy enforcement via a shared key cache, resulting in ciphertext that can be decrypted to multiple different plaintexts. To remediate this issue, users should upgrade to version 3.3.1, 4.0.5 or above.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| PyPI | aws-encryption-sdk | 3.3.1 | GHSA-v638-38fc-rhfv |
| PyPI | aws-encryption-sdk | 4.0.5 | GHSA-v638-38fc-rhfv |
| PyPI | aws-encryption-sdk | 3.3.1, 4.0.5 | PYSEC-2026-2387 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| AWS | AWS Encryption SDK for Python | 2 – through 2.5.13 – through 3.3.04 – through 4.0.4 |
Weakness: CWE-757 · Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N
References
- https://aws.amazon.com/security/security-bulletins/2026-017-aws/ vendor-advisory
- https://github.com/aws/aws-encryption-sdk-python/releases/tag/v4.0.5 patch
- https://github.com/aws/aws-encryption-sdk-python/releases/tag/v3.3.1 patch
- https://github.com/aws/aws-encryption-sdk-python/security/advisories/GHSA-v638-38fc-rhfv third-party-advisory