vulnerability / NVI-00017714 / Revision 1
MCP Atlassian: DNS-rebinding TOCTOU bypass of the SSRF fix (CVE-2026-27826)
GitHub lists this reviewed advisory for mcp-atlassian. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
6.5 medium
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
mcp-atlassian
source listed< 0.22.0
### Summary GHSA-7r34-79r5-rcc9's fix added `validate_url_for_ssrf`, 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 SSRF mitigation is incomplete against DNS-rebinding. The other advisory `GHSA-xjgw-4wvw-rgm4` (file-write) is unrelated. Verified live (2026-06-27): neither a
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
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- GHSA-489g-7rxv-6c8q ↗
GitHub Advisory Database · vendor advisory
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Public revision history
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- Revision 1 ·
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