CVE-2026-77256: MCP Atlassian: OAuth refresh-token backup file is world-readable under default Unix umask
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.savetokenstofile, refreshtoken, accesstoken, and umask, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
MCP Atlassianto a version that resolves this vulnerability.Fixed in 0.22.0
Event History
Frequently Asked Questions
Who is exposed to this issue?
Deployments of MCP Atlassian before version 0.22.0 are exposed when the process umask allows other local users to read newly created files. The risk is local: another user on the same system may be able to read the OAuth backup file.
What could an attacker do with the exposed file?
The fallback file contains plaintext OAuth refresh and access tokens. A local user who reads it can retain Atlassian access through the refresh token.
Is the default configuration affected?
The file permissions are inherited from the process umask rather than being explicitly restricted. Common or permissive Unix umask configurations can make the file world-readable.
What should be done if an immediate upgrade is not possible?
Use a restrictive process umask so token backup files are not readable by other users, and restrict access to existing backup files containing tokens. Upgrade to version 0.22.0 when possible.