MCP Atlassian: SSRF redirect protection missing for basic-auth and OAuth authentication branches

Exploitation

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

CVSS

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

EPSS

• CVE-2026-77261: 0.37% estimated exploitation activity in the next 30 days; percentile 31.31 (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 makessrfsafehook() blocks HTTP redirects to private/internal IPs by validating the Location header before the client follows a 3xx response. The problem is that this hook is only attached in one of three authentication branches — the header-PAT path. Basic auth and OAuth branches skip it entirely, so if the connected Atlassian server returns a redirect to something like http://169.254.169.254/, the requests session follows it without complaint. This is an incomplete fix for GHSA-7r34-79r5-rcc9. The hook works fine when it's there — it just isn't there for most production auth configurations. Details In src/mcpatlassian/servers/dependencies.py, three branches construct a fetcher and call createandvalidate(). Only Branch 1 passes attachssrfhook=True: attachssrfhook defaults to False, so branches 2 and 3 silently skip the protection. The hook itself (makessrfsafehook) is straightforward — it checks response.isredirect, grabs the Location header, and calls validateurlforssrf() to…

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-6529-c226-h328

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-6529-c226-h328

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-6529-c226-h328

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# Patch Next advisory brief: CVE-2026-77261

Advisory: MCP Atlassian: SSRF redirect protection missing for basic-auth and OAuth authentication branches
IDs: CVE-2026-77261, GHSA-6529-c226-h328
Record: https://patchnext.com/advisories/cve-2026-77261 (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 7.1)
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-6529-c226-h328 (GitHub-reviewed advisory GHSA-6529-c226-h328 lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0)
- Verified: https://osv.dev/vulnerability/GHSA-6529-c226-h328 (OSV record GHSA-6529-c226-h328 lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0 (fixed))

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