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Medium, CVSS 6.5amended

MCP Atlassian: DNS-rebinding TOCTOU bypass of the SSRF fix (CVE-2026-27826)

CVE-2026-73497GHSA-489g-7rxv-6c8q

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (mcp-atlassian 0.22.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
6.5 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
EPSS
  • CVE-2026-73497: 0.38% estimated exploitation activity in the next 30 days; percentile 31.48 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary GHSA-7r34-79r5-rcc9's fix added validateurlforssrf, which resolves the attacker-controlled X-Atlassian-{Jira,Confluence}-Url header host once at middleware time and trusts the result. But the outbound request is later built with the raw hostname and re-resolves at connect time with no IP pinning. An attacker-controlled rebinding DNS name returns a public IP on the guard's lookup (validation passes) and 169.254.169.254 / an internal IP on the request's lookup (the socket connects there) → unauthenticated SSRF to cloud metadata / internal services on the patched build. Relationship to CVE-2026-27826 / GHSA-7r34-79r5-rcc9 (incomplete fix — please read first) This is an incomplete-fix sibling of the published GHSA-7r34-79r5-rcc9 (the X-Atlassian--Url header SSRF). That fix (PR #986/#1005) added a single middleware-time resolve + allowlist DNS-skip, but does not pin the validated IP to the connection — the fetcher re-resolves the raw hostname at connect time, so the documented…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-489g-7rxv-6c8q

  2. Revision 1 · created ·

    Published from osv record GHSA-489g-7rxv-6c8q

Agent brief

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# Patch Next advisory brief: CVE-2026-73497

Advisory: MCP Atlassian: DNS-rebinding TOCTOU bypass of the SSRF fix (CVE-2026-27826)
IDs: CVE-2026-73497, GHSA-489g-7rxv-6c8q
Record: https://patchnext.com/advisories/cve-2026-73497 (revision 2, source checked 26 Oct 2026, 13:46 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://osv.dev/vulnerability/GHSA-489g-7rxv-6c8q (OSV record GHSA-489g-7rxv-6c8q lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0 (fixed))
- Verified: https://github.com/advisories/GHSA-489g-7rxv-6c8q (GitHub-reviewed advisory GHSA-489g-7rxv-6c8q lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0)

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