CVE-2026-77271: Atlassian MCP path traversal bypass leading to RCE

CVE-2026-77271 · Severity: high · CVSS 4 · Published 2026-09-22

MCP (Model Context Protocol) for Atlassian is a server that integrates with Confluence to handle file downloads and attachments. A flaw in the path validation logic allows an authenticated attacker with Confluence write access to overwrite Python source files within the application directory, leading to remote code execution when the service restarts. This bypasses a previous security patch and affects all patched versions.

Technologies: mcp-atlassian (PyPI). Vendors: PyPI.

Quick answers

Is CVE-2026-77271 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-77271 being exploited in the wild.
How severe is CVE-2026-77271?
High severity, with a CVSS score of 4, 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-2026-77271?
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-2026-77271 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-77271?
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
    pip install "mcp-atlassian>=0.22.0"

Technical details

The vulnerability is an incomplete path traversal fix in validate_safe_path() (mcp_atlassian/utils/io.py). When no explicit base_dir argument is provided, the function defaults to os.getcwd() (typically /app in containers). The is_relative_to() check then permits any path within the working directory, including Python source modules, to pass validation. Two call sites in confluence/attachments.py (download_attachment and download_content_attachments functions) invoke validate_safe_path() without specifying a base_dir, allowing attackers to write arbitrary .py files to the application source tree. On process restart, the malicious module code executes. The attack requires Confluence credentials with write access and network access to the MCP HTTP server (which binds to 0.0.0.0 with no authentication by default).

Affected products

  • Atlassian MCP 0.17.0 through 0.21.0

Identifiers

  • CVE-2026-77271
  • GHSA-6vmq-24h2-pj7j
  • PYSEC-2026-4087

Timeline

  • 2026-09-22: disclosed: GHSA-6vmq-24h2-pj7j published

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