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CVE-2026-77274 – SSRF Protection Bypass – mcp-atlassian < 0.22.0

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Summary

CVE-2026-77274 is a Server-Side Request Forgery (SSRF) protection bypass affecting mcp-atlassian, a Model Context Protocol (MCP) server that connects AI agents to Atlassian Jira and Confluence. Versions prior to 0.22.0 contain a URL-parsing inconsistency in the validate_url_for_ssrf function that lets an attacker craft a URL which passes SSRF validation as pointing to an external host while the underlying HTTP client actually connects to an internal or loopback address. The issue carries a CVSS v4.0 base score of 8.8 (High) and requires no authentication or user interaction.

Technical details

  • Root cause: validate_url_for_ssrf() parses URLs using Python’s urllib.parse.urlparse(), while the actual outbound request is made via the requests library’s Session, which interprets URL authority/userinfo syntax differently — creating a parser mismatch (backslash-before-userinfo confusion).
  • Trigger conditions: An attacker supplies a crafted URL (e.g., http://127.0.0.1:[email protected]) via the X-Atlassian-Jira-Url or X-Atlassian-Confluence-Url HTTP headers used in the header-based Jira/Confluence authentication flow. The validation layer evaluates the URL as pointing to the external host (www.baidu.com), while requests percent-encodes the backslash and routes the connection to the attacker-specified internal target (127.0.0.1:6666).
  • Attack vector: Network — no authentication and no user interaction are required; the attacker only needs the ability to reach the mcp-atlassian HTTP endpoint and set custom headers.
  • Impact: Successful exploitation allows the server process to make outbound requests to internal/loopback network resources that should be unreachable, enabling internal network reconnaissance, access to internal services, and potential exposure of sensitive data returned to the attacker (High confidentiality impact, Low integrity impact per the CVSS vector).

Affected software

  • Product: mcp-atlassian (vendor: sooperset)
  • Vulnerable versions: all versions prior to 0.22.0
  • Fixed version: 0.22.0

Severity

  • CVSS v4.0 Base Score: 8.8 (High)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
  • CWE-918: Server-Side Request Forgery (SSRF)

Mitigation and recommended actions

  • Immediate: Upgrade mcp-atlassian to version 0.22.0 or later, which fixes the URL-parsing inconsistency between the SSRF validation logic and the HTTP request layer.
  • If patching is not immediately possible:
    • Restrict network access to the mcp-atlassian HTTP endpoint to trusted clients only (e.g., via network segmentation, firewall rules, or an authenticating reverse proxy).
    • Strip or validate the X-Atlassian-Jira-Url and X-Atlassian-Confluence-Url headers at a gateway/proxy layer before they reach mcp-atlassian, disallowing userinfo/backslash characters in the authority component.
    • Monitor outbound traffic from the mcp-atlassian host for unexpected connections to loopback or internal address ranges.

References

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