# CVE-2026-77250: MCP Atlassian OAuth fallback token storage plaintext exposure

Source: https://junglewise.ai/threats/cve-2026-77250-mcp-atlassian-oauth-fallback-token-storage-plaintext-exposure  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-22. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-77250 · Severity: medium · CVSS 6.1 · Published 2026-09-22

MCP Atlassian stores OAuth tokens (access and refresh credentials) in a plaintext file in the user's home directory with world-readable permissions. Any user or process on the same system with access to the home directory can steal these tokens and impersonate the account to Atlassian APIs, enabling account compromise and unauthorized access to Atlassian services.

Technologies: [mcp-atlassian (PyPI)](https://junglewise.ai/threats/technologies/mcp-atlassian). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-77250 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-77250 being exploited in the wild.

**How severe is CVE-2026-77250?** Medium severity, with a CVSS score of 6.1, published 22 September 2026.

**Which products and versions are affected?** mcp-atlassian (PyPI) < 0.22.0, ECOSYSTEM:introduced=0,fixed=0.22.0.

**Is there a fix for CVE-2026-77250?** Yes. mcp-atlassian (PyPI): upgrade to 0.22.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-77250 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-77250?** Check whether you run mcp-atlassian (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- mcp-atlassian (PyPI): upgrade to 0.22.0 or later

  ```sh
  pip install "mcp-atlassian>=0.22.0"
  ```


## Technical details

The vulnerability exists in the OAuthConfig._save_tokens() method, which writes OAuth tokens (access_token and refresh_token) to ~/.mcp-atlassian/oauth-&lt;client_id&gt;.json with default umask permissions (mode 0o664) instead of restrictive owner-only permissions (0o600). The fallback file is created unconditionally for backwards compatibility even when keyring storage succeeds, and no chmod or secure open mode is applied. An attacker with local filesystem access can read this file, extract the tokens, and use the refresh token to maintain persistent access to the victim's Atlassian account. The vulnerability affects shared systems, containers, developer workstations, and CI runners.

## Affected products

- Atlassian MCP Atlassian <UNKNOWN>

## Identifiers

- CVE-2026-77250
- GHSA-g5xv-mhgm-v5f6
- PYSEC-2026-4094

## Timeline

- 2026-09-22: disclosed

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- [MCP Atlassian path traversal in upload_attachment](https://junglewise.ai/threats/cve-2026-77266-mcp-atlassian-path-traversal-in-upload-attachment)
- [sooperset mcp-atlassian path traversal in confluence_upload_attachment](https://junglewise.ai/threats/cve-2026-77262-sooperset-mcp-atlassian-path-traversal-in-confluence-upload)