# CVE-2026-77266: MCP Atlassian path traversal in upload_attachment

Source: https://junglewise.ai/threats/cve-2026-77266-mcp-atlassian-path-traversal-in-upload-attachment  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-22. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-77266 · Severity: medium · CVSS 6.5 · Published 2026-09-22

MCP Atlassian is a tool that integrates AI agents with Atlassian products (Jira and Confluence) via the Model Context Protocol. The upload_attachment functions in both modules lack path validation, allowing an authenticated attacker to read and exfiltrate arbitrary files from the server—including system passwords, API keys, OAuth tokens, and SSH keys—by uploading files from sensitive paths like /etc/passwd or /proc/self/environ.

Technologies: [mcp-atlassian (PyPI)](https://junglewise.ai/threats/technologies/mcp-atlassian). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-77266 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-77266 being exploited in the wild.

**How severe is CVE-2026-77266?** Medium severity, with a CVSS score of 6.5, published 22 September 2026.

**Which products and versions are affected?** mcp-atlassian (PyPI) < 0.22.0, ECOSYSTEM:introduced=0,fixed=0.22.0.

**Is there a fix for CVE-2026-77266?** Yes. mcp-atlassian (PyPI): upgrade to 0.22.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-77266 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-77266?** Check whether you run mcp-atlassian (PyPI) 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.

## How to fix

- mcp-atlassian (PyPI): upgrade to 0.22.0 or later

  ```sh
  pip install "mcp-atlassian>=0.22.0"
  ```


## Technical details

This is a path traversal vulnerability in the upload_attachment() functions of both the Jira and Confluence modules (mcp_atlassian/jira/attachments.py and mcp_atlassian/confluence/attachments.py). The functions accept a user-controlled file_path parameter and open the file for reading without calling validate_safe_path(), unlike the corresponding download functions which were protected in a prior fix (GHSA-xjgw-4wvw-rgm4). An authenticated MCP client can supply arbitrary paths (e.g., /etc/passwd, /proc/self/environ, ~/.mcp-atlassian/oauth-*.json) causing the server process to read and transmit the file's contents to the remote Atlassian instance as an attachment. No special privileges beyond standard MCP tool access are required. The vulnerability is reachable over the network in HTTP-mode deployments and locally in stdio-mode, affecting both jira_upload_attachment and confluence_upload_attachment MCP tools.

## Affected products

- Atlassian MCP Atlassian up to v0.21.1

## Identifiers

- CVE-2026-77266
- GHSA-mfv2-4wvm-9pgp
- PYSEC-2026-4097

## Timeline

- 2026-09-22: disclosed: GHSA-mfv2-4wvm-9pgp published
- 2026: other: CVE-2026-77266 assigned

## Related threats

- [Atlassian MCP reflected XSS in OAuth setup callback handler](https://junglewise.ai/threats/cve-2026-77272-atlassian-mcp-reflected-xss-in-oauth-setup-callback-handler)
- [Atlassian MCP path traversal in upload_attachment allows arbitrary file read](https://junglewise.ai/threats/cve-2026-77269-atlassian-mcp-path-traversal-in-upload-attachment-allows)
- [Atlassian MCP insecure OAuth token file permissions](https://junglewise.ai/threats/cve-2026-77268-atlassian-mcp-insecure-oauth-token-file-permissions)
- [sooperset mcp-atlassian path traversal in confluence_upload_attachment](https://junglewise.ai/threats/cve-2026-77262-sooperset-mcp-atlassian-path-traversal-in-confluence-upload)
- [MCP Atlassian arbitrary file read via confluence_upload_attachment](https://junglewise.ai/threats/cve-2026-77259-mcp-atlassian-arbitrary-file-read-via-confluence-upload)