MCP Atlassian: SSRF via DNS Rebinding in Header-Based Authentication Flow

Exploitation

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

CVSS

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

EPSS

• CVE-2026-77265: 0.29% estimated exploitation activity in the next 30 days; percentile 21.75 (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 SSRF protection for header-based authentication uses a validate-then-use pattern vulnerable to DNS rebinding. validateurlforssrf resolves the hostname via DNS and checks that the resolved IP is globally routable. However, the actual HTTP request happens later, during which the DNS record may have changed to point to an internal IP (127.0.0.1, 169.254.169.254, etc.). The SSRF redirect hook only validates redirect targets, not the initial connection. Details The vulnerability spans main.py (validation) and dependencies.py (use). Step 1 -- URL validation at middleware time: In src/mcpatlassian/servers/main.py:524-531, the URL from X-Atlassian-Jira-Url is validated: if jiraurlstr: ssrferror = validateurlforssrf(jiraurlstr) if ssrferror:

blocked validateurlforssrf (src/mcpatlassian/utils/urls.py:113-116) resolves DNS and checks isglobal: dnserror = checkdnsresolution(hostname) if dnserror: return dnserror Step 2 -- HTTP request happens later with a separate DNS resolution:…

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-49xv-9743-pw8w

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-49xv-9743-pw8w

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-49xv-9743-pw8w

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-77265

Advisory: MCP Atlassian: SSRF via DNS Rebinding in Header-Based Authentication Flow
IDs: CVE-2026-77265, GHSA-49xv-9743-pw8w
Record: https://patchnext.com/advisories/cve-2026-77265 (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 5.9)
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-49xv-9743-pw8w (GitHub-reviewed advisory GHSA-49xv-9743-pw8w lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0)
- Verified: https://osv.dev/vulnerability/GHSA-49xv-9743-pw8w (OSV record GHSA-49xv-9743-pw8w lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0 (fixed))

Commands are suggestions: review each one before running it.