Medium severity · published Sep 22, 2026
CVE-2026-77250
MCP Atlassian: OAuth fallback token storage writes plaintext access and refresh tokens with group-readable permissions
6.1
CVSS
0.1%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
High
Integrity
Low
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.1% · higher than 2% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MC
mcp-atlassian · sooperset
< 0.22.0 · source: vendor
MA
Mcp Atlassian · Mcp-atlassian
before 0.22.0 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-77250
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-77250
Patch
https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460
Issue Tracking
https://github.com/sooperset/mcp-atlassian/pull/1448
Release Notes
https://github.com/sooperset/mcp-atlassian/releases/tag/v0.22.0
Exploit
https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-g5xv-mhgm-v5f6
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