CVE-2026-77258: MCP Atlassian Path Traversal Vulnerability

CVE-2026-77258 Overview

MCP Atlassian is a Model Context Protocol (MCP) server that bridges AI assistants with Atlassian products including Confluence and Jira. Versions prior to 0.22.0 contain a path traversal vulnerability [CWE-22] in the upload_attachment function located in src/mcp_atlassian/confluence/attachments.py. The function accepts a caller-controlled file_path parameter and opens the referenced server-local file without restricting the path to the workspace directory. A permitted Confluence MCP caller can supply an arbitrary absolute or traversal path, causing the server to read the target file and upload it as a Confluence attachment. This exposes any file readable by the MCP server process to the attacker.

Critical Impact
An authenticated MCP caller can exfiltrate arbitrary server-local files (configuration, credentials, source code) by uploading them as Confluence attachments.

Affected Products

MCP Atlassian versions prior to 0.22.0
Deployments exposing the Confluence MCP upload_attachment tool
Environments where the MCP server process has access to sensitive local files

Discovery Timeline

2026-09-22 - CVE-2026-77258 published to NVD
2026-09-23 - Last updated in NVD database

Technical Details for CVE-2026-77258

Vulnerability Analysis

The MCP Atlassian server exposes an upload_attachment tool that lets MCP clients attach files to Confluence pages. The pre-patch implementation accepted any string as file_path, converted relative paths to absolute paths using os.path.abspath, and then opened the resulting file directly. No check confirmed that the resolved path remained inside the intended workspace directory. A caller with permission to invoke the tool can therefore reference sensitive files such as /etc/passwd, ~/.aws/credentials, SSH private keys, or .env files. The server reads the file with its own privileges and uploads the contents as a Confluence attachment, which the attacker can subsequently download. The scope change (S:C) in the CVSS vector reflects that the impacted resource (the local filesystem) lies outside the vulnerable component's authorization boundary.

Root Cause

The root cause is missing path canonicalization and workspace confinement. The vulnerable code trusted the caller-supplied file_path and did not validate that the resolved path fell within an approved directory tree, enabling directory traversal and absolute-path abuse.

Attack Vector

Exploitation requires network access to the MCP server and low-privilege authentication as a permitted Confluence MCP caller. No user interaction is needed. The attacker calls upload_attachment with a file_path pointing to any file readable by the server process, then retrieves the uploaded attachment through Confluence.

python

            return {"success": False, "error": "No file path provided"}

        try:
-            # Convert to absolute path if relative
-            if not os.path.isabs(file_path):
-                file_path = os.path.abspath(file_path)
+            # Confine the upload source to the workspace before it is read: reject
+            # traversal/absolute paths that escape CWD (arbitrary file read /
+            # exfiltration via a caller-supplied file_path).
+            file_path = str(validate_safe_path(file_path))

            # Check if file exists
            if not os.path.exists(file_path):

Source: GitHub Commit b041733 — the patch replaces the naive absolute-path conversion with a validate_safe_path call that rejects traversal sequences and paths escaping the current working directory.

Detection Methods for CVE-2026-77258

Indicators of Compromise

Confluence attachments uploaded via MCP whose original filenames match sensitive system files (for example, passwd, shadow, id_rsa, .env, credentials).
MCP server logs showing upload_attachment invocations with absolute paths or paths containing ../ sequences.
Unexpected file-read operations by the MCP service account targeting directories outside the intended workspace.

Detection Strategies

Audit Confluence attachment metadata for uploads originating from the MCP integration and correlate against expected content types.
Instrument the MCP server to log the resolved file_path value passed to upload_attachment and alert on paths outside the workspace root.
Review authentication logs for MCP callers issuing bursts of upload_attachment requests, which may indicate automated exfiltration.

Monitoring Recommendations

Enable filesystem auditing (auditd, Sysmon FileCreate, EDR file-access telemetry) on the host running MCP Atlassian, scoped to sensitive directories.
Forward MCP server logs and Confluence attachment audit events to a centralized SIEM for correlation.
Alert on any read of secret material (private keys, cloud credentials, .env files) by the MCP service process.

How to Mitigate CVE-2026-77258

Immediate Actions Required

Upgrade MCP Atlassian to version 0.22.0 or later, which introduces the validate_safe_path workspace confinement.
Rotate any credentials, API tokens, or private keys stored on hosts running vulnerable MCP Atlassian instances.
Review Confluence attachments created by MCP integrations since deployment and remove any containing sensitive server-local content.

Patch Information

The fix is delivered in MCP Atlassian v0.22.0 via Pull Request #1448. Full technical context is available in GitHub Security Advisory GHSA-93xw-j965-9mx3.

Workarounds

Run the MCP Atlassian server under a dedicated low-privilege user account with filesystem access restricted to a single workspace directory.
Deploy the MCP server inside a container or chroot with only the workspace directory mounted, preventing reads outside that scope.
Restrict MCP caller permissions so that only trusted clients can invoke upload_attachment until the upgrade is applied.

bash

# Upgrade MCP Atlassian to the patched release
pip install --upgrade "mcp-atlassian>=0.22.0"

# Verify the installed version
python -c "import mcp_atlassian, importlib.metadata; print(importlib.metadata.version('mcp-atlassian'))"