CVE-2026-77250: mcp-atlassian Plaintext Token Storage Vulnerability
Summary
CVE-2026-77250: When OAuth tokens are saved, MCP Atlassian always writes a plaintext fallback copy under ~/.mcp-atlassian/oauth-.json. Affects mcp-atlassian versions < 0.22.0. Fixed in 0.22.0. How to fix ↓
Check if this vulnerability affects your application
Upload a manifest or SBOM and we'll show whether you're affected, plus every other risky package in the same scan.
No signup required · Results in about 60 seconds
Background
mcp-atlassian is a Python package that facilitates interaction with Atlassian's APIs, enabling developers to automate tasks and manage resources within Atlassian products. The package supports OAuth for authentication, which is a widely used standard for secure access delegation. However, a vulnerability has been identified in the way it handles OAuth tokens, specifically in the storage of fallback copies of these tokens in plaintext format.
Vulnerability Detail
The vulnerability arises from the mcp-atlassian package's method of saving OAuth tokens. When tokens are stored, a plaintext fallback copy is created in the user's home directory with group-readable permissions. This occurs due to the use of the process default umask, which results in the file being created with mode 0664. As a result, access and refresh tokens are exposed to local users within the same group and any processes that can read the home directory. This could lead to unauthorized access to Atlassian APIs, allowing attackers to exploit the tokens until they are revoked or expire.
How To Fix
Latest published version: 0.23.1 as of 23 Oct 2026
pip install --upgrade "mcp-atlassian==0.23.1"Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
0.22.0
This is the first release that contains the fix.
pip install --upgrade "mcp-atlassian==0.22.0"Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, you can manually change the permissions of the fallback token file after it is created to restrict access. Use the following command to set the file permissions to owner-only: 'chmod 600 ~/.mcp-atlassian/oauth-<client_id>.json'. However, this is not a permanent solution and updating the package is recommended.
Conclusion
The mcp-atlassian package has a vulnerability that exposes OAuth tokens in plaintext format with group-readable permissions. It is crucial to update to version 0.22.0 or later to mitigate this risk. Until then, implement the suggested workarounds to protect sensitive information.
See every vulnerability recorded for mcp-atlassian →
FAQ
CVE-2026-77250 is a vulnerability in the mcp-atlassian package that allows plaintext storage of OAuth tokens with group-readable permissions.
If your application uses mcp-atlassian and is affected by this vulnerability, local users or processes could access sensitive OAuth tokens, potentially leading to unauthorized API access.
You can use the Vulert playground at Vulert Scanner to check if your application is affected by this vulnerability without requiring any signup.
If an immediate update is not possible, consider changing the permissions of the token file to restrict access as a temporary workaround.
The CVSS score of this vulnerability is 6.1, indicating a moderate level of severity.
References
Related vulnerabilities
Recent vulnerabilities recorded for mcp-atlassian.
