CVE-2026-77270

MCP Atlassian: Arbitrary File Read via Upload Attachment Tools

# Convert to absolute path if relative
if not os.path.isabs(file_path):
    file_path = os.path.abspath(file_path)

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

# src/mcp_atlassian/confluence/attachments.py:223
validate_safe_path(target_path)  # <-- used for downloads

# src/mcp_atlassian/confluence/attachments.py:272
validate_safe_path(target_dir)   # <-- used for downloads

# Convert to absolute path if relative
if not os.path.isabs(file_path):
    file_path = os.path.abspath(file_path)

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

# src/mcp_atlassian/servers/jira.py:1607-1673
# The update_issue tool accepts an "attachments" parameter (file paths)
# which flows to jira.update_issue() -> self.upload_attachments() -> self.upload_attachment()

# src/mcp_atlassian/jira/issues.py:1133-1136
if "attachments" in kwargs and kwargs["attachments"]:
    attachments_result = self.upload_attachments(
        issue_key, kwargs["attachments"]
    )

# src/mcp_atlassian/servers/confluence.py:1356-1363
confluence_fetcher = await get_confluence_fetcher(ctx)
result = confluence_fetcher.upload_attachment(
    content_id=content_id,
    file_path=file_path,  # passed directly, no validation
    comment=comment,
    minor_edit=minor_edit,
)

# MCP tool invocation (via JSON-RPC)
{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "confluence_upload_attachment",
    "arguments": {
      "content_id": "12345",
      "file_path": "/etc/passwd"
    }
  },
  "id": 1
}

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "update_issue",
    "arguments": {
      "issue_key": "PROJ-123",
      "fields": "{}",
      "attachments": "["/etc/passwd", "/home/deploy/.env"]"
    }
  },
  "id": 2
}

• Arbitrary file read: Any file readable by the server process can be exfiltrated via both Confluence and Jira upload paths
• Credential theft: Environment files (.env), SSH keys (/.ssh/), OAuth tokens (/.mcp-atlassian/), and application configs can be stolen
• Prompt injection amplification: Malicious content in Jira/Confluence can trigger file exfiltration via the AI assistant
• Write tools require authentication: The @check_write_access decorator enforces READ_ONLY_MODE, but when write access is allowed, any authenticated user can upload any file
• Both services affected: The vulnerability exists independently in both the Confluence and Jira attachment upload code paths

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-77270 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.22.0); upgrading removes the vulnerable code path.

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Call validate_safe_path before reading the file in both upload methods:

Confluence fix (src/mcp_atlassian/confluence/attachments.py):

def upload_attachment(self, content_id, file_path, comment=None, minor_edit=True):
    if not content_id or not file_path:
        return {"success": False, "error": "Missing parameters"}

    try:
        # Validate path does not escape base directory
        validated_path = validate_safe_path(file_path)
        file_path = str(validated_path)

        if not os.path.exists(file_path):
            return {"success": False, "error": f"File not found: {file_path}"}
        # ... rest of upload logic

Jira fix (src/mcp_atlassian/jira/attachments.py):

def upload_attachment(self, issue_key, file_path):
    if not issue_key or not file_path:
        return {"success": False, "error": "Missing parameters"}

    try:
        # Validate path does not escape base directory
        validated_path = validate_safe_path(file_path)
        file_path = str(validated_path)

        if not os.path.exists(file_path):
            return {"success": False, "error": f"File not found: {file_path}"}
        # ... rest of upload logic

1. What is CVE-2026-77270? CVE-2026-77270 is a medium-severity path traversal vulnerability in mcp-atlassian (pip), affecting versions < 0.22.0. It is fixed in 0.22.0. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-77270? CVE-2026-77270 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of mcp-atlassian are affected by CVE-2026-77270? mcp-atlassian (pip) versions < 0.22.0 is affected.
4. Is there a fix for CVE-2026-77270? Yes. CVE-2026-77270 is fixed in 0.22.0. Upgrade to this version or later.
5. Is CVE-2026-77270 exploitable, and should I be worried? Whether CVE-2026-77270 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-77270 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-77270? Upgrade mcp-atlassian to 0.22.0 or later.

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