mcp-atlassian · Model Context Protocol Python SDK: Client fetched server-chosen $ref URLs while validating tool results against output
Affects mcp-atlassianSource GCVE Database
Not known to be exploited · CVSS 6.5 Medium : upgrade to 0.23.1_1 when convenient.
Data as of 30 Oct 2026, 08:32 UTC
Thin evidence
One scorer or none| CNA (GitHub_M) | CVSS 3.1 | 6.5 |
|---|
- Patch
- Available – fixed in 0.23.1_1
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 27 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.
What to do
Upgrade mcp-atlassian to 0.23.1_1.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Homebrewmcp-atlassianpkg:brew/mcp-atlassianOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
Upgrade the MCP Python SDK client to version 1.30.0 (1.x) or 2.2.0 (2.x) or later, where the vulnerability is fixed by restricting $ref resolution to within the schema document only. Until upgrading, only call tools on trusted servers. As a partial mitigation, avoid calling tools whose outputSchema contains an $id or any $ref/$dynamicRef that does not start with '#'.
Description
The Model Context Protocol (MCP) Python SDK client versions 1.10.0 through 1.29.1 and 2.0.0 through 2.1.1 have a vulnerability where the client fetches server-chosen $ref URLs during tool output schema validation. This causes the client to synchronously request external HTTP, HTTPS, or local file URLs on every tool call, potentially stalling the client if the target is unresponsive. The issue is fixed in versions 1.30.0 and 2.2.0 or later by restricting reference resolution to within the schema document only.
References
- github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-rwrf-2pqf-9j8j (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk/pull/3394 (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk/pull/3396 (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk/commit/5ebdfed4060d8e5b11b8e2348f86bad4d1fb8836 (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk/commit/6705402e246dc4eb1fcdf4d9902b78d3c9c36e1b (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0 (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0 (opens in a new tab)