Key commitment policy bypass via shared key cache in AWS Encryption SDK for Python

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Summary

CVECVE-2026-6550
StatePUBLISHED
AssignerAMZN
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-20 20:16:49 UTC
Updated2026-04-20 20:16:49 UTC
DescriptionCryptographic 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.

Risk And Classification

Primary CVSS: v4.0 5.7 MEDIUM from ff89ba41-3aa1-4d27-914a-91399e9639e5

CVSS:4.0/AV:L/AC:H/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Problem Types: CWE-757 | CWE-757 CWE-757 Selection of Less-Secure algorithm during negotiation ('algorithm downgrade')

VersionSourceTypeScoreSeverityVector
4.0ff89ba41-3aa1-4d27-914a-91399e9639e5Secondary5.7MEDIUMCVSS:4.0/AV:L/AC:H/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/C...
4.0CNACVSS5.7MEDIUMCVSS:4.0/AV:L/AC:H/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
3.1ff89ba41-3aa1-4d27-914a-91399e9639e5Secondary4.7MEDIUMCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N
3.1CNACVSS4.7MEDIUMCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N

CVSS v4.0 Breakdown

Attack Vector
Local
Attack Complexity
High
Attack Requirements
Present
Privileges Required
Low
User Interaction
None
Confidentiality
None
Integrity
High
Availability
None
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

CVSS:4.0/AV:L/AC:H/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA AWS AWS Encryption SDK For Python affected 2 2.5.1 custom Not specified
CNA AWS AWS Encryption SDK For Python affected 3 3.3.0 custom Not specified
CNA AWS AWS Encryption SDK For Python affected 4 4.0.4 custom Not specified

References

ReferenceSourceLinkTags
github.com/aws/aws-encryption-sdk-python/releases/tag/v3.3.1 ff89ba41-3aa1-4d27-914a-91399e9639e5 github.com
github.com/aws/aws-encryption-sdk-python/releases/tag/v4.0.5 ff89ba41-3aa1-4d27-914a-91399e9639e5 github.com
github.com/aws/aws-encryption-sdk-python/security/advisories/GHSA-v638-3... ff89ba41-3aa1-4d27-914a-91399e9639e5 github.com
aws.amazon.com/security/security-bulletins/2026-017-aws ff89ba41-3aa1-4d27-914a-91399e9639e5 aws.amazon.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: 1seal.org (en)

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