CVE-2026-77274: MCP Atlassian SSRF Vulnerability

CVE-2026-77274 Overview

CVE-2026-77274 is a Server-Side Request Forgery (SSRF) vulnerability in MCP Atlassian, a Model Context Protocol (MCP) server for Atlassian Confluence and Jira. Versions prior to 0.22.0 contain a flaw in the validate_url_for_ssrf function. The validator parses the URL authority differently from the underlying Requests HTTP client during header-based Jira and Confluence authentication flows. Attackers can craft a URL that passes external hostname validation while the HTTP client connects to an internal host. This enables server-side requests to protected internal network resources. The issue is tracked as [CWE-918] and is fixed in version 0.22.0.

Critical Impact
Attackers can bypass SSRF protections and reach internal network resources through the MCP Atlassian server, exposing sensitive metadata endpoints and internal services.

Affected Products

MCP Atlassian versions prior to 0.22.0
MCP Atlassian deployments integrating Jira via header-based authentication
MCP Atlassian deployments integrating Confluence via header-based authentication

Discovery Timeline

2026-09-22 - CVE-2026-77274 published to NVD
2026-09-23 - Last updated in NVD database

Technical Details for CVE-2026-77274

Vulnerability Analysis

The vulnerability resides in the validate_url_for_ssrf function used in the header-based authentication flow for Jira and Confluence URLs. The function parses the URL authority component using different logic than the Python Requests library's connection layer. This parser mismatch is the root of the flaw.

When a URL contains a backslash character in the authority, the validator treats one hostname as authoritative while Requests interprets a different hostname when opening the TCP connection. An attacker supplies a URL that appears external to the validator but resolves to an internal address at the transport layer. The MCP server then issues an authenticated HTTP request against internal infrastructure.

Successful exploitation exposes cloud metadata services, internal admin panels, and unrouted management APIs. The vulnerability is remotely triggerable without authentication or user interaction at the MCP interface.

Root Cause

The root cause is parser differential handling of the backslash character in URL authority components. RFC 3986 and browser-adjacent parsers treat \ inconsistently, and the validator normalized the authority differently than the connection layer that actually dispatched the request. This is a classic time-of-check to time-of-use gap between validation and network dispatch, categorized under [CWE-918] Server-Side Request Forgery.

Attack Vector

An attacker submits a crafted Jira or Confluence base URL to the MCP Atlassian server through the header-based authentication flow. The URL is structured so the authority component contains a backslash that shifts the effective host between parsers. The validator sees an allowlisted external hostname while the Requests connection opens a socket to an attacker-chosen internal host. The MCP server then forwards authentication headers and receives responses from the internal target.

No authenticated code execution primitive is required at the target service beyond what SSRF affords. Reference GitHub Security Advisory GHSA-hgcf-4mq8-5266 for the maintainer analysis.

python

# Patch excerpt from src/mcp_atlassian/confluence/attachments.py
# Source: https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460

try:
    # Confine the upload source to the workspace before it is read: reject
    # traversal/absolute paths that escape CWD (arbitrary file read /
    # exfiltration via a caller-supplied file_path).
    file_path = str(validate_safe_path(file_path))

    # Check if file exists
    if not os.path.exists(file_path):

The broader commit hardens URL validation, transport, SSRF checks, and authorization filters. See GitHub Pull Request #1448 for the full change set.

Detection Methods for CVE-2026-77274

Indicators of Compromise

Outbound HTTP requests from the MCP Atlassian process to RFC1918 addresses, loopback, or cloud metadata endpoints such as 169.254.169.254
Jira or Confluence base URLs containing backslash characters (\) in the authority component within MCP configuration or request logs
Unexpected authentication headers appearing in traffic to internal services that do not host Atlassian products

Detection Strategies

Inspect MCP Atlassian request logs for URLs where the parsed hostname differs from the resolved connection destination
Enable egress logging on the MCP server host and alert on connections to internal CIDR ranges or metadata IPs
Deploy WAF or reverse proxy rules that reject URLs containing raw or percent-encoded backslashes in the authority

Monitoring Recommendations

Monitor MCP Atlassian for version strings below 0.22.0 in deployment inventories
Track outbound DNS queries and TCP connections initiated by the MCP service to non-Atlassian domains
Alert on 200-class responses returned from cloud metadata endpoints reached through the MCP process

How to Mitigate CVE-2026-77274

Immediate Actions Required

Upgrade MCP Atlassian to version 0.22.0 or later, available at GitHub Release v0.22.0
Audit MCP Atlassian configuration for user-supplied Jira and Confluence base URLs and reject any containing backslashes
Rotate any credentials or API tokens used by the MCP Atlassian service if SSRF activity is suspected

Patch Information

The fix is delivered in MCP Atlassian 0.22.0 via commit b041733473f95119dd539542a43c280737a8e460. The patch replaces the previous URL authority handling and adds broader hardening across attachment, transport, SSRF, and authorization paths. See the GitHub Commit Details for the complete diff.

Workarounds

Place the MCP Atlassian server in a network segment that cannot route to internal management interfaces or cloud metadata services
Enforce an egress allowlist restricting outbound connections to known Atlassian Cloud or Data Center hostnames only
Terminate MCP-initiated HTTP requests through a forward proxy that performs strict URL parsing and rejects malformed authorities

bash

# Upgrade MCP Atlassian to the patched release
pip install --upgrade "mcp-atlassian>=0.22.0"

# Verify the installed version
python -c "import importlib.metadata; print(importlib.metadata.version('mcp-atlassian'))"