MCP Atlassian: Insecure File Permissions on OAuth Token Storage

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.5 · CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

EPSS

• CVE-2026-77268: 0.15% estimated exploitation activity in the next 30 days; percentile 4.45 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The OAuth token fallback file storage in OAuthConfig.savetokenstofile() creates token files containing access tokens, refresh tokens, and cloud IDs with default filesystem permissions (typically 0644 on Linux, world-readable). Any local user on a shared system can read these files to obtain full Atlassian API credentials, enabling unauthorized access to the victim's Jira and Confluence data. Details The vulnerability exists in src/mcpatlassian/utils/oauth.py in the savetokenstofile method. Step 1 -- Directory created without restrictive permissions: At line 402-403, the token directory is created with mkdir(existok=True) which uses the default umask (typically creating directories with mode 0755): Step 2 -- Token file written with default permissions: At line 417-418, the token file containing sensitive credentials is written using open() with no explicit mode, inheriting default umask permissions (typically 0644 on Linux): Step 3 -- The file contains full API credentials:…

Published by the source

22 Sep 2026, 20:35 UTC

Last modified by the source

1 Oct 2026, 17:56 UTC

Source last checked

26 Oct 2026, 13:54 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-4596-2p6p-28cv

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-4596-2p6p-28cv

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-4596-2p6p-28cv

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# Patch Next advisory brief: CVE-2026-77268

Advisory: MCP Atlassian: Insecure File Permissions on OAuth Token Storage
IDs: CVE-2026-77268, GHSA-4596-2p6p-28cv
Record: https://patchnext.com/advisories/cve-2026-77268 (revision 3, source checked 26 Oct 2026, 13:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: mcp-atlassian 0.22.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI mcp-atlassian: affected < 0.22.0; fixed in 0.22.0

## Suggested inspection (read-only)
- `python -m pip show mcp-atlassian`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on mcp-atlassian.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-4596-2p6p-28cv (GitHub-reviewed advisory GHSA-4596-2p6p-28cv lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0)
- Verified: https://osv.dev/vulnerability/GHSA-4596-2p6p-28cv (OSV record GHSA-4596-2p6p-28cv lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0 (fixed))

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