Summary
MCP Atlassian: Unauthenticated arbitrary local file read via uploadattachment filepath, chained with missing auth on streamable-http transport
In the documented multi-user HTTP deployment (--transport streamable-http with global operator Atlassian credentials), sooperset/mcp-atlassian exposes all tools to unauthenticated network clients, and the upload_attachment tool reads an attacker-supplied file_path with no path validation. Chained, an unauthenticated network attacker reads arbitrary files on the MCP server host (e.g. /proc/self/environ → the operator's Atlassian API token + .env secrets, ~/.ssh/id_rsa, /etc/passwd) by uploading them to an attacker-chosen page/issue and reading them back.
Details
Missing authentication (transport):
- streamable-http binds
0.0.0.0by default (src/mcp_atlassian/__init__.py:151). - The OAuth-proxy auth provider is opt-in (
ATLASSIAN_OAUTH_PROXY_ENABLE, default false), somain_mcpis built withauth=None(src/mcp_atlassian/servers/main.py:724-731, 813-817). UserTokenMiddleware._parse_auth_headersetsauth_validation_erroronly for a malformed Authorization header; a request with no Authorization header passes through (main.py:416-446, 582-595)._get_fetcherthen falls through to the global credential fallback using the operator's.envAtlassian token (src/mcp_atlassian/servers/dependencies.py:644-676).check_write_accessgates only on read-only mode, not auth → read and write tools reachable.
Arbitrary file read (sink):
upload_attachment'sfile_pathflows unsanitized intoopen(file_path, 'rb'), Confluencesrc/mcp_atlassian/confluence/attachments.py:477(fromservers/confluence.py:1294-1369); Jirasrc/mcp_atlassian/jira/attachments.py:386(fromservers/jira.py:1609-1673). Novalidate_safe_path/ allowlist (contrast the download flow, hardened after CVE-2026-27825).
Proof of Concept
# unauthenticated (no Authorization header) against a default streamable-http deployment:
tools/call upload_attachment { "file_path": "/proc/self/environ", "page_id": "<attacker-chosen>" }
# then read it back:
tools/call download_attachment { ... } # returns the bytes (base64) -> operator's ATLASSIAN token + .env secrets
Affected
mcp-atlassian <= 0.21.1.
Impact
Unauthenticated arbitrary local file read on the MCP server host, including the operator's Atlassian API token and .env secrets, a boundary the Atlassian-scoped tool must not cross, plus unauthenticated use of every read/write Atlassian tool as the operator's (often admin) principal. Distinct from GHSA-xjgw-4wvw-rgm4 (file write via download_path) and GHSA-7r34-79r5-rcc9 (URL-header SSRF).
Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.
CVE-2026-77248 has a CVSS score of 8.6 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.22.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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See it in your environmentNew to Kodem? Get a demo →Remediation advice
Require authentication on the streamable-http transport by default (do not fall back to operator global credentials for unauthenticated requests); apply validate_safe_path/allowlist to file_path in upload_attachment as the download flow already does.
Frequently Asked Questions
- What is CVE-2026-77248? CVE-2026-77248 is a high-severity path traversal vulnerability in mcp-atlassian (pip), affecting versions < 0.22.0. It is fixed in 0.22.0. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- How severe is CVE-2026-77248? CVE-2026-77248 has a CVSS score of 8.6 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of mcp-atlassian are affected by CVE-2026-77248? mcp-atlassian (pip) versions < 0.22.0 is affected.
- Is there a fix for CVE-2026-77248? Yes. CVE-2026-77248 is fixed in 0.22.0. Upgrade to this version or later.
- Is CVE-2026-77248 exploitable, and should I be worried? Whether CVE-2026-77248 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-77248 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-77248? Upgrade
mcp-atlassianto 0.22.0 or later.