MCP Atlassian: Arbitrary File Read & Exfiltration (Confused Deputy) in JIRA update_issue

Exploitation

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

CVSS

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

EPSS

• CVE-2026-77255: 0.46% estimated exploitation activity in the next 30 days; percentile 39.83 (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 A critical Confused Deputy (Arbitrary File Read & Exfiltration) vulnerability in the Atlassian MCP server (Python) allows an AI agent to exfiltrate sensitive host files and environment secrets. By providing absolute system paths to the attachments parameter of the updateissue tool, an agent can force the privileged MCP process to read and upload any file it has access to—including its own environment variables and host configuration—directly to a Jira ticket. Details The vulnerability is located in the updateissue tool handler. The attachments parameter accepts a list of file paths that are passed directly to the Jira API's upload method without any sanitization or validation. Specifically, the implementation fails to: 1. Restrict paths to a safe workspace: It accepts absolute paths starting with /. 2. Prevent directory traversal: It does not filter for ../ sequences. 3. Validate ownership: It allows the process to read system-level files (like /proc/self/environ) that the…

Published by the source

22 Sep 2026, 20:34 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-2xj6-xx86-cwwc

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-2xj6-xx86-cwwc

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-2xj6-xx86-cwwc

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# Patch Next advisory brief: CVE-2026-77255

Advisory: MCP Atlassian: Arbitrary File Read & Exfiltration (Confused Deputy) in JIRA update_issue
IDs: CVE-2026-77255, GHSA-2xj6-xx86-cwwc
Record: https://patchnext.com/advisories/cve-2026-77255 (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: High (CVSS 8.6)
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-2xj6-xx86-cwwc (GitHub-reviewed advisory GHSA-2xj6-xx86-cwwc lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0)
- Verified: https://osv.dev/vulnerability/GHSA-2xj6-xx86-cwwc (OSV record GHSA-2xj6-xx86-cwwc lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0 (fixed))

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