PYSEC-2026-4084

Vulnerability from pysec - Published: 2026-10-01 16:38 - Updated: 2026-10-01 17:10
VLAI
Details

Summary

The UserTokenMiddleware extracts URLs from X-Atlassian-Jira-Url and X-Atlassian-Confluence-Url HTTP headers and passes them directly to API client constructors without any SSRF validation.

Affected Package

  • Ecosystem: PyPI
  • Package: mcp-atlassian
  • Affected versions: all versions before fix commit 5cd697dfce91
  • Patched versions: >= commit 5cd697dfce91

Details

In main.py, _process_authentication_headers() extracts URLs from ASGI headers without validation. In dependencies.py, get_jira_fetcher() creates JiraConfig with url=jira_url_header directly. There is no validate_url call, no IP range check, no hostname validation.

The fix adds URL validation to some paths but the header-based URL extraction in _process_authentication_headers() still passes raw URLs through. The derived config objects use the header URL directly and the fetcher makes HTTP requests to that URL.

PoC

jira_url_header = headers.get(b"x-atlassian-jira-url")
jira_url_str = jira_url_header.decode("latin-1") if jira_url_header else None
service_headers["X-Atlassian-Jira-Url"] = jira_url_str

Steps to reproduce: 1. git clone https://github.com/sooperset/mcp-atlassian /tmp/mcp-atlassian_test 2. cd /tmp/mcp-atlassian_test && git checkout 5cd697dfce91~1 3. pip install -e . 4. python3 poc.py

Expected output:

VULNERABILITY CONFIRMED
User-supplied URLs from HTTP headers passed directly to JiraConfig/JiraFetcher with no SSRF validation

Impact

An attacker can set X-Atlassian-Jira-Url: http://169.254.169.254/latest/meta-data/ to access AWS instance metadata, or target any internal service. The server makes authenticated HTTP requests to the attacker-specified URL.

Suggested Remediation

Validate all user-supplied URLs against an allowlist of permitted hostnames or reject private/loopback/link-local IP ranges. Consider requiring server-side configuration of allowed Atlassian instance URLs.

Severity
8.3 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N
Impacted products
Name purl
mcp-atlassian pkg:pypi/mcp-atlassian
Aliases
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "mcp-atlassian",
        "purl": "pkg:pypi/mcp-atlassian"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.22.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.1.1",
        "0.1.10",
        "0.1.11",
        "0.1.12",
        "0.1.13",
        "0.1.14",
        "0.1.15",
        "0.1.16",
        "0.1.2",
        "0.1.3",
        "0.1.4",
        "0.1.6",
        "0.1.7",
        "0.1.8",
        "0.1.9",
        "0.10.0",
        "0.10.1",
        "0.10.2",
        "0.10.3",
        "0.10.4",
        "0.10.5",
        "0.10.6",
        "0.11.0",
        "0.11.1",
        "0.11.10",
        "0.11.11",
        "0.11.12",
        "0.11.2",
        "0.11.2a2",
        "0.11.3",
        "0.11.4",
        "0.11.5",
        "0.11.6",
        "0.11.7",
        "0.11.8",
        "0.11.9",
        "0.12.0",
        "0.13.0",
        "0.13.1",
        "0.14.0",
        "0.14.1",
        "0.14.2",
        "0.14.3",
        "0.15.0",
        "0.16.0",
        "0.16.1",
        "0.17.0",
        "0.18.0",
        "0.18.1",
        "0.19.0",
        "0.2.0",
        "0.2.1",
        "0.2.2",
        "0.2.3",
        "0.2.4",
        "0.2.5",
        "0.2.6",
        "0.20.0",
        "0.20.1",
        "0.21.0",
        "0.21.1",
        "0.3.0",
        "0.3.1",
        "0.4.0",
        "0.5.0",
        "0.6.0",
        "0.6.1",
        "0.6.2",
        "0.6.3",
        "0.6.4",
        "0.6.5",
        "0.7.0",
        "0.7.1",
        "0.8.0",
        "0.8.1",
        "0.8.2",
        "0.8.3",
        "0.8.4",
        "0.9.0"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-77267",
    "GHSA-5wf4-jqxh-8gm3"
  ],
  "details": "### Summary\n\nThe `UserTokenMiddleware` extracts URLs from `X-Atlassian-Jira-Url` and `X-Atlassian-Confluence-Url` HTTP headers and passes them directly to API client constructors without any SSRF validation.\n\n### Affected Package\n\n- **Ecosystem:** PyPI\n- **Package:** mcp-atlassian\n- **Affected versions:** all versions before fix commit 5cd697dfce91\n- **Patched versions:** \u003e= commit 5cd697dfce91\n\n### Details\n\nIn `main.py`, `_process_authentication_headers()` extracts URLs from ASGI headers without validation. In `dependencies.py`, `get_jira_fetcher()` creates `JiraConfig` with `url=jira_url_header` directly. There is no `validate_url` call, no IP range check, no hostname validation.\n\nThe fix adds URL validation to some paths but the header-based URL extraction in `_process_authentication_headers()` still passes raw URLs through. The derived config objects use the header URL directly and the fetcher makes HTTP requests to that URL.\n\n### PoC\n\n```python\njira_url_header = headers.get(b\"x-atlassian-jira-url\")\njira_url_str = jira_url_header.decode(\"latin-1\") if jira_url_header else None\nservice_headers[\"X-Atlassian-Jira-Url\"] = jira_url_str\n```\n\n**Steps to reproduce:**\n1. `git clone https://github.com/sooperset/mcp-atlassian /tmp/mcp-atlassian_test`\n2. `cd /tmp/mcp-atlassian_test \u0026\u0026 git checkout 5cd697dfce91~1`\n3. `pip install -e .`\n4. `python3 poc.py`\n\n**Expected output:**\n```\nVULNERABILITY CONFIRMED\nUser-supplied URLs from HTTP headers passed directly to JiraConfig/JiraFetcher with no SSRF validation\n```\n\n### Impact\n\nAn attacker can set `X-Atlassian-Jira-Url: http://169.254.169.254/latest/meta-data/` to access AWS instance metadata, or target any internal service. The server makes authenticated HTTP requests to the attacker-specified URL.\n\n### Suggested Remediation\n\nValidate all user-supplied URLs against an allowlist of permitted hostnames or reject private/loopback/link-local IP ranges. Consider requiring server-side configuration of allowed Atlassian instance URLs.",
  "id": "PYSEC-2026-4084",
  "modified": "2026-10-01T17:10:30.108379Z",
  "published": "2026-10-01T16:38:36.058700Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-5wf4-jqxh-8gm3"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-77267"
    },
    {
      "type": "WEB",
      "url": "https://github.com/sooperset/mcp-atlassian/pull/1448"
    },
    {
      "type": "WEB",
      "url": "https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/sooperset/mcp-atlassian"
    },
    {
      "type": "WEB",
      "url": "https://github.com/sooperset/mcp-atlassian/releases/tag/v0.22.0"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/mcp-atlassian"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-5wf4-jqxh-8gm3"
    }
  ],
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "mcp-atlassian has an incomplete SSRF remediation"
}



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