Summary
AWS Encryption SDK (ESDK) for Python is a client-side encryption library. An issue exists where, under certain circumstances, a specific cryptographic algorithm downgrade in the caching layer 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
Workarounds
If a customer requires operating multiple instances of the Python ESDK each with differently configured key commitment policies, they must not share a key cache.
References
If there are any questions or comments about this advisory, contact AWS Security through the vulnerability reporting page or directly via email to [email protected]. Please do not create a public GitHub issue.
Acknowledgement
Thanks to 1seal.org for collaborating on this issue through the coordinated vulnerability disclosure process.
Impact
This issue requires all of the following conditions to be true: (1) Two ESDK for Python clients with different commitment policies share a single CachingCryptoMaterialsManager instance within the same process. (2) The client with the weaker commitment policy encrypts first, warming the cache. (3) Both clients use matching encryption contexts. (4) Both clients use the pre-configured default algorithm suite.
These conditions may occur during a migration from ESDK for Python v1 to newer versions, as v1 did not support key commitment.
When the weaker-policy client encrypts first, the cache stores encryption materials that do not enforce key commitment. Subsequent callers, including those configured to require key commitment, are served these cached materials instead of generating new ones that satisfy their policy. This results in encryption without key commitment, meaning the same ciphertext can be validly decrypted to different plaintexts under different keys (the "Invisible Salamanders" issue; see https://github.com/google/security-research/security/advisories/GHSA-wqgp-vphw-hphf). A threat actor who controls ciphertext can cause a recipient to decrypt a message different from what the sender encrypted, breaking message integrity.
CVE-2026-6550 has a CVSS score of 4.7 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.3.1, 4.0.5); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
This issue has been addressed in ESDK for Python versions 3.3.1 and 4.0.5. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes.
Frequently Asked Questions
- What is CVE-2026-6550? CVE-2026-6550 is a medium-severity security vulnerability in aws-encryption-sdk (pip), affecting versions >= 2.0.0, < 3.3.0. It is fixed in 3.3.1, 4.0.5.
- How severe is CVE-2026-6550? CVE-2026-6550 has a CVSS score of 4.7 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of aws-encryption-sdk are affected by CVE-2026-6550? aws-encryption-sdk (pip) versions >= 2.0.0, < 3.3.0 is affected.
- Is there a fix for CVE-2026-6550? Yes. CVE-2026-6550 is fixed in 3.3.1, 4.0.5. Upgrade to this version or later.
- Is CVE-2026-6550 exploitable, and should I be worried? Whether CVE-2026-6550 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-6550 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-6550?
- Upgrade
aws-encryption-sdkto 3.3.1 or later - Upgrade
aws-encryption-sdkto 4.0.5 or later
- Upgrade