CVE-2026-6550: CWE-757 Selection of Less-Secure algorithm during negotiation ('algorithm downgrade') in AWS AWS Encryption SDK for Python
Bulletin ID: 2026-017-AWS Scope: AWS Content Type: Important (requires attention) Publication Date: 2026/04/20 12:45 PM PDT Description: AWS Encryption SDK (ESDK) for Python is a client-side encryption library. We identified CVE-2026-6550, which describes an issue with a key commitment policy bypass via shared key cache. 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. Impacted versions: - From 2.0 to 2.5.1 - From 3.0 to 3.3.0 - From 4.0 to 4.0.4 Please refer to the article below for the most up-to-date and complete information related to this AWS Security Bulletin.
AI Analysis
Technical Summary
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.
Potential Impact
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.
Mitigation Recommendations
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/.
CVE-2026-6550: CWE-757 Selection of Less-Secure algorithm during negotiation ('algorithm downgrade') in AWS AWS Encryption SDK for Python
Description
Bulletin ID: 2026-017-AWS Scope: AWS Content Type: Important (requires attention) Publication Date: 2026/04/20 12:45 PM PDT Description: AWS Encryption SDK (ESDK) for Python is a client-side encryption library. We identified CVE-2026-6550, which describes an issue with a key commitment policy bypass via shared key cache. 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. Impacted versions: - From 2.0 to 2.5.1 - From 3.0 to 3.3.0 - From 4.0 to 4.0.4 Please refer to the article below for the most up-to-date and complete information related to this AWS Security Bulletin.
CVSS v3.1
Score 4.7medium
Affected software
AWS
AWS Encryption SDK for Python
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
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.
Potential Impact
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.
Mitigation Recommendations
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/.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- AMZN
- Date Reserved
- 2026-04-17T20:06:20.299Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Is Cloud Service
- true
- Vendor Advisory Urls
- [{"url":"https://aws.amazon.com/security/security-bulletins/2026-017-aws/","vendor":"AWS"}]
Threat ID: 69e6827f19fe3cd2cd2c9b8d
Added to database: 04/20/2026, 19:46:07 UTC
Last enriched: 06/05/2026, 19:29:11 UTC
Last updated: 09/14/2026, 10:01:33 UTC
Views: 200
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