CVE-2026-77250 MCP Atlassian: OAuth fallback token storage writes plaintext access and refresh tokens with group-readable permissions
Local attackers can read plaintext OAuth tokens from insecurely stored files to hijack Atlassian accounts.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-77250?
CVE-2026-77250 is a medium-severity vulnerability in sooperset mcp-atlassian, published on 22 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, OAuthConfig writes a plaintext fallback file containing access and refresh tokens under the user's .mcp-atlassian directory using process-default permissions. On systems with a permissive umask, same-group or other local users and processes can read the persisted tokens and reuse the associated Atlassian access. The advisory traces the vulnerable input and processing flow through OAuthConfig._save_tokens, ~/.mcp-atlassian/oauth-<client_id>.json, access_token, and refresh_token, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.
Weakness: CWE-312
Which versions are affected by CVE-2026-77250?
3 open source packages ship an affected version, including mcp-atlassian. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
mcp-atlassian PyPI | All versions | 0.22.0 |
mcp-atlassian PyPI | All versions | 0.22.0 |
mcp-atlassian PyPI | All versions | 0.22.0 |
Products include Mcp-Atlassian Mcp Atlassian.
How do I fix CVE-2026-77250?
Upgrade mcp-atlassian to 0.22.0 or later.
Is CVE-2026-77250 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77250 exists.
Other vulnerabilities in sooperset mcp-atlassian
- CVE-2026-77244 [mcp-atlassian] Authentication bypass in HTTP transport: AtlassianOpaqueTokenVerifier accepts any non-empty token
- CVE-2026-77254 MCP Atlassian: Unauthenticated HTTP MCP requests can use globally configured Jira and Confluence credentials
- CVE-2026-27825 MCP Atlassian has an arbitrary file write leading to arbitrary code execution via unconstrained download_path in confluence_download_attachment
- CVE-2026-77243 MCP Atlassian: ENABLED_TOOLS / Toolset authorization bypass
- CVE-2026-77274 MCP Atlassian: SSRF Protection Bypass
Sources
Also known as GHSA-g5xv-mhgm-v5f6, PYSEC-2026-4094.