CVE-2026-48529 json
GitHub MCP Server: Lockdown mode singleton in HTTP server causes cross-user GraphQL client confusion
published 2026-06-25 4 mo ago modified 2026-10-25 14 d ago also GHSA-pjp5-fpmr-3349 , GO-2026-5779 , EUVD-2026-39809
- cvss
- 6.0
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.2%
- EPSS 0.2% chance of exploitation in 30 days, percentile 5%
- public exploits
- 0
- none known
Summary
GitHub MCP Server is GitHub's official MCP Server. From 0.22.0 until 1.1.2, when running in HTTP mode with --lockdown-mode enabled, the RepoAccessCache is implemented as a process-global singleton initialized with the first authenticated user's GraphQL client. All subsequent requests from different users share this singleton and their lockdown-related GraphQL queries are executed using the first user's credentials. The singleton is never updated to reflect later users' tokens. This vulnerability is fixed in 1.1.2.
Patch / fix
- go github.com/github/github-mcp-server 1.1.2
- govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1
opensuse advisories openSUSE-SU-2026:21483-1
CISA SSVC
- Exploitation
- Proof of concept is public
- Automatable
- no
- Technical impact
- partial
- Assessed
- 4 mo ago
Exploit prediction
0.17% chance of exploitation in the next 30 days, higher than 5% of all scored CVEs (FIRST EPSS, 2026-11-08).
Exploits and checks
- github.com https://github.com/github/github-mcp-server/security/advisories/GHSA-pjp5-fpmr-3349 referenced PoC, tagged "exploit" by a source, unverified
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 6.0 | CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:L/A:L |
| GitHub | 3.1 | 6.0 | CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:L/A:L |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| go | github.com/github/github-mcp-server | >=0.22.0, <1.1.2 |
1.1.2 |
Affected products
- github github-mcp-server
Classification
- Weakness
-
- CWE-284 Improper Access Control
References
-
github.com
/github/github-mcp-server/security/advisories/GHSA-pjp5-fpmr-3349
exploit, web, advisory
-
github.com
/github/github-mcp-server
package
Sources
- CVE List CVE-2026-48529
- GitHub Advisory GHSA-pjp5-fpmr-3349
- NVD CVE-2026-48529
- OSV GO-2026-5779
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