MCP Atlassian: Path traversal in upload_attachment allows arbitrary file read and exfiltration via MCP tool call

Exploitation

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

CVSS

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

EPSS

• CVE-2026-77266: 0.50% estimated exploitation activity in the next 30 days; percentile 42.88 (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 uploadattachment functions in both the Jira and Confluence modules accept a user-controlled filepath parameter and open the specified file for reading without calling validatesafepath(). An authenticated MCP client can supply an arbitrary path such as /etc/passwd or /proc/self/environ, causing the server process to read and transmit the file's contents to the remote Atlassian instance as an attachment. This is an incomplete fix relative to GHSA-xjgw-4wvw-rgm4: the downloadattachment and downloadissueattachments paths were hardened with validatesafepath(), but the upload direction was left unguarded in both the Jira and Confluence modules. --- Details Affected functions: | File | Function | Line | |------|----------|------| | src/mcpatlassian/jira/attachments.py | uploadattachment() | ~372–415 | | src/mcpatlassian/confluence/attachments.py | uploadattachment() | ~62–108 | | src/mcpatlassian/confluence/attachments.py | uploadattachmentdirect() | ~476–477 | Jira — vulnerable…

Published by the source

22 Sep 2026, 20:35 UTC

Last modified by the source

1 Oct 2026, 17:55 UTC

Source last checked

26 Oct 2026, 13:54 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-mfv2-4wvm-9pgp

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-mfv2-4wvm-9pgp

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-mfv2-4wvm-9pgp

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# Patch Next advisory brief: CVE-2026-77266

Advisory: MCP Atlassian: Path traversal in upload_attachment allows arbitrary file read and exfiltration via MCP tool call
IDs: CVE-2026-77266, GHSA-mfv2-4wvm-9pgp
Record: https://patchnext.com/advisories/cve-2026-77266 (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 6.5)
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-mfv2-4wvm-9pgp (GitHub-reviewed advisory GHSA-mfv2-4wvm-9pgp lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0)
- Verified: https://osv.dev/vulnerability/GHSA-mfv2-4wvm-9pgp (OSV record GHSA-mfv2-4wvm-9pgp lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0 (fixed))

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