CVE-2026-77266 MCP Atlassian: Path traversal in upload_attachment allows arbitrary file read and exfiltration via MCP tool call
An attacker with attachment access can read arbitrary server files and exfiltrate them via Jira or Confluence using the upload_attachment tool.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-77266?
CVE-2026-77266 is a medium-severity path traversal vulnerability in sooperset mcp-atlassian, published on 22 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, upload_attachment accepts absolute paths and traversal sequences without constraining the resolved path to the server workspace. An MCP caller with attachment access can read a chosen server-local file and exfiltrate it through Jira or Confluence. The advisory traces the vulnerable input and processing flow through upload_attachment, file_path, and path traversal, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.
Weakness: CWE-22
Which versions are affected by CVE-2026-77266?
3 open source packages ship an affected version, including mcp-atlassian. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
mcp-atlassian PyPI | All versions | 0.22.0 |
mcp-atlassian PyPI | All versions | 0.22.0 |
mcp-atlassian PyPI | All versions | 0.22.0 |
Products include Mcp-Atlassian Mcp Atlassian.
How do I fix CVE-2026-77266?
Upgrade mcp-atlassian to 0.22.0 or later.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-77266 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77266 exists.
Other vulnerabilities in sooperset mcp-atlassian
- CVE-2026-77244 [mcp-atlassian] Authentication bypass in HTTP transport: AtlassianOpaqueTokenVerifier accepts any non-empty token
- CVE-2026-77254 MCP Atlassian: Unauthenticated HTTP MCP requests can use globally configured Jira and Confluence credentials
- CVE-2026-27825 MCP Atlassian has an arbitrary file write leading to arbitrary code execution via unconstrained download_path in confluence_download_attachment
- CVE-2026-77243 MCP Atlassian: ENABLED_TOOLS / Toolset authorization bypass
- CVE-2026-77274 MCP Atlassian: SSRF Protection Bypass
Sources
Also known as GHSA-mfv2-4wvm-9pgp, PYSEC-2026-4097.