CVE-2026-125271 json
AWS API MCP Server Security Policy Bypass via Incorrect Operation Name Normalization
published yesterday modified yesterday also EUVD-2026-121327 , GHSA-4wq9-grf3-qg2p
Unreviewed: the maintainers' own advisory
Published by the maintainers on their GitHub repository awslabs/mcp. GitHub has not reviewed it into the GitHub Advisory Database, so the affected packages and versions are the maintainers' word. Read the full advisory on GitHub.
- cvss
- 7.8
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.4%
- EPSS 0.4% chance of exploitation in 30 days, percentile 31%
- public exploits
- 0
- none known
Summary
Incorrect normalization of operation names in the custom security policy enforcement in awslabs aws-api-mcp-server before 1.5.1 might allow an actor to execute AWS API operations across AWS services that the operator's security policy was configured to deny or require elicitation for, via calls to operations whose names contain consecutive capital letters.
To remediate this issue, users should upgrade to version 1.5.1.
Patch / fix
Is CVE-2026-125271 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerExploit prediction
0.37% chance of exploitation in the next 30 days, higher than 31% of all scored CVEs (FIRST EPSS, 2026-11-11).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 7.8 | CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H |
| CNA | 4.0 | 8.5 | CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N |
| CNA | 4.0 | 8.5 | CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/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 |
Affected products
- AWS aws-api-mcp-server
Classification
References
-
pypi.org
/project/awslabs.aws-api-mcp-server/1.5.1/
release-notes, patch
-
aws.amazon.com
/security/security-bulletins/2026-176-aws/
vendor-advisory
-
github.com
/awslabs/mcp/security/advisories/GHSA-4wq9-grf3-qg2p
third-party-advisory, advisory
Sources
- CVE List CVE-2026-125271
- NVD CVE-2026-125271
- Maintainer advisory GHSA-4wq9-grf3-qg2p
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.
The maintainers of awslabs/mcp published their own advisory on GitHub. Reviewed sources take precedence over it.