CVE-2026-4270 json
AWS API MCP File Access Restriction Bypass
published 7mo ago modified 4mo ago also GHSA-2cpp-j2fc-qhp7 , PYSEC-2026-162 , EUVD-2026-12474
- cvss
- 5.5
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.1%
- EPSS 0.1% chance of exploitation in 30 days, percentile 3%
- public exploits
- 0
- none known
Summary
Improper Protection of Alternate Path exists in the no-access and workdir feature of the AWS API MCP Server versions >= 0.2.14 and < 1.3.9 on all platforms may allow the bypass of intended file access restriction and expose arbitrary local file contents in the MCP client application context.
To remediate this issue, users should upgrade to version 1.3.9.
Patch / fix
- pypi awslabs-aws-api-mcp-server 1.3.9
- AWS AWS API MCP Server 1.3.9
Is CVE-2026-4270 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 7mo ago
Exploit prediction
0.14% chance of exploitation in the next 30 days, higher than 3% of all scored CVEs (FIRST EPSS, 2026-11-09).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 5.5 | CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N |
| CNA | 4.0 | 6.8 | CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N |
| CNA | 4.0 | 6.8 | CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/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 |
| GitHub | 3.1 | 5.5 | CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| pypi | awslabs-aws-api-mcp-server | >=0.2.14, <1.3.9 |
1.3.9 |
Affected products
- AWS AWS API MCP Server
Classification
- Weakness
-
- CWE-424 Improper Protection of Alternate Path
References
-
pypi.org
/project/awslabs.aws-api-mcp-server/1.3.9/
patch, third-party-advisory, advisory
-
aws.amazon.com
/security/security-bulletins/2026-007-AWS/
vendor-advisory, advisory
-
github.com
/awslabs/mcp/security/advisories/GHSA-2cpp-j2fc-qhp7
web
-
nvd.nist.gov
/vuln/detail/CVE-2026-4270
advisory
-
aws.amazon.com
/security/security-bulletins/2026-007-AWS
web
-
github.com
/awslabs/mcp
package
-
github.com
/pypa/advisory-database/tree/main/vulns/awslabs-aws-api-mcp-server/PYSEC-2026-162.yaml
web
-
pypi.org
/project/awslabs.aws-api-mcp-server/1.3.9
web
-
github.com
/advisories/GHSA-2cpp-j2fc-qhp7
advisory
Sources
- CVE List CVE-2026-4270
- GitHub Advisory GHSA-2cpp-j2fc-qhp7
- NVD CVE-2026-4270
- OSV PYSEC-2026-162
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.