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CVE-2026-116686VulnerabilityPublished

mcp-atlassian · Model Context Protocol Python SDK: Client fetched server-chosen $ref URLs while validating tool results against output

Affects mcp-atlassianSource GCVE Database

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Authoritative record:CVE-2026-116686· Medium 6.5

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

CVSS 3.1 base score
6.5Medium
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (GitHub_M)CVSS 3.16.5
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:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 27 Oct 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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

ProductAffectedFixed in
Homebrewmcp-atlassianpkg:brew/mcp-atlassianOther threatsAffected
  • >=0.11.9 <0.23.1_1
Fixed in
  • 0.23.1_1

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

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