# CVE-2026-77256: MCP Atlassian insecure file permissions in OAuth token storage

Source: https://junglewise.ai/threats/cve-2026-77256-mcp-atlassian-is-a-model-context-protocol-mcp-server-for  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-22. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-77256 · Severity: info · Published 2026-09-22

MCP Atlassian is a Model Context Protocol server that connects AI models to Atlassian products like Jira and Confluence. Before version 0.22.0, OAuth refresh and access tokens are saved to a backup file with permissions inherited from the process umask, potentially allowing other local users on the system to read the file and gain unauthorized access to Atlassian accounts.

Technologies: [Sooperset Mcp-Atlassian](https://junglewise.ai/threats/technologies/sooperset-mcp-atlassian). Vendors: [Sooperset](https://junglewise.ai/threats/vendors/sooperset).

## Quick answers

**Is CVE-2026-77256 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-77256 being exploited in the wild.

**How severe is CVE-2026-77256?** Informational severity, published 22 September 2026.

**Which products and versions are affected?** Sooperset Mcp-Atlassian prior to 0.22.0.

**Is there a fix for CVE-2026-77256?** A patch was published on 2026-07-10: Fix merged in version 0.22.0 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-77256 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-77256?** Check whether you run Sooperset Mcp-Atlassian 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.

## Technical details

The vulnerability exists in OAuthConfig._save_tokens_to_file, which writes plaintext OAuth refresh and access tokens to a file with default permissions based on the process umask. Under permissive umask configurations, other local users can read this backup file and extract the refresh token to maintain Atlassian access. The fix in version 0.22.0 restricts file permissions to prevent unauthorized local access.

## Affected products

- sooperset MCP Atlassian prior to 0.22.0

## Timeline

- 2026-09-22: disclosed
- 2026-07-10: patched: Fix merged in version 0.22.0

## References

- [https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460](https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460)
- [https://github.com/sooperset/mcp-atlassian/pull/1448](https://github.com/sooperset/mcp-atlassian/pull/1448)

## Related threats

- [sooperset mcp-atlassian path traversal in validate_safe_path](https://junglewise.ai/threats/cve-2026-124503-a-vulnerability-was-identified-in-sooperset-mcp-atlassian-up-to)
- [MCP Atlassian HTTP transport authentication bypass](https://junglewise.ai/threats/cve-2026-77254-mcp-atlassian-is-a-model-context-protocol-mcp-server-for)
- [MCP Atlassian path traversal in attachment upload](https://junglewise.ai/threats/cve-2026-77258-mcp-atlassian-is-a-model-context-protocol-mcp-server-for)
- [MCP Atlassian authorization bypass in projects and spaces filter](https://junglewise.ai/threats/cve-2026-77252-mcp-atlassian-is-a-model-context-protocol-mcp-server-for)
- [MCP Atlassian SSRF validation bypass via DNS rebinding](https://junglewise.ai/threats/cve-2026-77242-mcp-atlassian-is-a-model-context-protocol-mcp-server-for)