CVE-2026-77256 MCP Atlassian: OAuth refresh-token backup file is world-readable under default Unix umask
Local attackers can read world-readable OAuth token files to hijack Atlassian accounts due to insecure default file permissions.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-77256?
CVE-2026-77256 is a high-severity vulnerability in sooperset mcp-atlassian, published on 22 Sep 2026. Any signed-in user can exploit it over the 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, the plaintext OAuth fallback file containing refresh and access tokens is written with permissions inherited from the process umask. Under common or permissive configurations, other local users can read the backup and retain Atlassian access through the refresh token. The advisory traces the vulnerable input and processing flow through OAuthConfig._save_tokens_to_file, refresh_token, access_token, and umask, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.
Weakness: CWE-732
Which versions are affected by CVE-2026-77256?
It affects 1 product.
Products include Mcp-Atlassian Mcp Atlassian.
How do I fix CVE-2026-77256?
No fix has been published for CVE-2026-77256 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-77256 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77256 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-76pr-5669-3xf5.