# CVE-2026-6550: Key commitment policy bypass via shared key cache in AWS Encryption SDK for Python

> An authenticated local attacker can bypass key commitment policies via a shared key cache, allowing ciphertext to decrypt to multiple plaintexts.

- **Severity:** Medium 5.7 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Apr 2026
- **Updated:** 20 Apr 2026
- **Also known as:** GHSA-v638-38fc-rhfv, PYSEC-2026-2387

## What is CVE-2026-6550?

CVE-2026-6550 is a medium-severity vulnerability in AWS Encryption SDK for Python, published on 20 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### 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.

Weakness: CWE-757 (Selection of Less-Secure Algorithm During Negotiation)

## Which versions are affected by CVE-2026-6550?

5 open source packages ship an affected version, including aws-encryption-sdk.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `aws-encryption-sdk` | PyPI | From 2.0.0 | 3.3.1, 4.0.5 |
| `aws-encryption-sdk` | PyPI | From 2.0.0 | 3.3.1 |
| `aws-encryption-sdk` | PyPI | From 2.0.0 | 3.3.1 |
| `aws-encryption-sdk` | PyPI | From 4.0.0 | 4.0.5 |
| `aws-encryption-sdk` | PyPI | From 4.0.0 | 4.0.5 |

## How do I fix CVE-2026-6550?

Upgrade aws-encryption-sdk to a fixed version for your release line: 3.3.1 or 4.0.5.

## Is CVE-2026-6550 being exploited?

There is no known exploitation of CVE-2026-6550 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-6550 and fix it if it is affected.

What it is: CVE-2026-6550 is a medium-severity vulnerability in AWS Encryption SDK for Python, published on 20 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-6550 in the wild and no public exploit code.

Affected packages and fixed versions:
- aws-encryption-sdk (PyPI): affected from 2.0.0; fixed in 3.3.1, 4.0.5
- aws-encryption-sdk (PyPI): affected from 2.0.0; fixed in 3.3.1
- aws-encryption-sdk (PyPI): affected from 2.0.0; fixed in 3.3.1
- aws-encryption-sdk (PyPI): affected from 4.0.0; fixed in 4.0.5
- aws-encryption-sdk (PyPI): affected from 4.0.0; fixed in 4.0.5

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-6550/ (Markdown: https://insights.sbomify.com/CVE-2026-6550/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-6550
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6550
- OSV: https://osv.dev/vulnerability/CVE-2026-6550

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-6550/
Summaries are generated and may contain mistakes; the official description above is the record.