Summary
MCP Atlassian: Arbitrary File Read & Exfiltration (Confused Deputy) in JIRA update_issue
A critical Confused Deputy (Arbitrary File Read & Exfiltration) vulnerability in the Atlassian MCP server (Python) allows an AI agent to exfiltrate sensitive host files and environment secrets. By providing absolute system paths to the attachments parameter of the update_issue tool, an agent can force the privileged MCP process to read and upload any file it has access to, including its own environment variables and host configuration, directly to a Jira ticket.
Details
The vulnerability is located in the update_issue tool handler. The attachments parameter accepts a list of file paths that are passed directly to the Jira API's upload method without any sanitization or validation.
Specifically, the implementation fails to:
1. Restrict paths to a safe workspace: It accepts absolute paths starting with /.
2. Prevent directory traversal: It does not filter for ../ sequences.
3. Validate ownership: It allows the process to read system-level files (like /proc/self/environ) that the calling agent is normally forbidden from accessing due to sandbox restrictions.
Because the MCP server typically runs with higher privileges than the AI agent (holding the JIRA_API_TOKEN and having wider filesystem access), it acts as a "Confused Deputy," performing exfiltration on behalf of a restricted agent.
PoC
To reproduce the vulnerability in an environment where the agent is sandboxed (e.g., as a restricted Unix user) but the MCP server has host-level access:
1. Exfiltrate MCP Secrets:
The agent calls the update_issue tool with the following payload:
{
"issue_key": "SECURITY-1",
"attachments": ["/proc/self/environ"]
}
Result: The MCP server reads its own process environment, containing the JIRA_API_TOKEN and other sensitive keys in plain text, and attaches it to the Jira issue.
2. Exfiltrate Host Configuration:
The agent calls the tool to target global assistant settings:
{
"issue_key": "SECURITY-1",
"attachments": ["/home/hermes/.hermes/config.yaml"]
}
Result: The host's global configuration file (containing tokens for GitLab, Slack, and other services) is successfully exfiltrated to the cloud.
Impact
* Critical Credential Theft: Immediate exposure of the JIRA_API_TOKEN and any other secrets injected into the MCP server's environment.
* Arbitrary File Access: Total exfiltration of any data the host user running the MCP server can read (SSH keys, databases, local source code).
* Privilege Escalation & Lateral Movement: Attackers can move from a restricted AI sandbox to full host-system control by stealing tokens or configuration files.
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-2026-77255 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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Frequently Asked Questions
- What is CVE-2026-77255? CVE-2026-77255 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-2026-77255? CVE-2026-77255 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-2026-77255? mcp-atlassian (pip) versions < 0.22.0 is affected.
- Is there a fix for CVE-2026-77255? Yes. CVE-2026-77255 is fixed in 0.22.0. Upgrade to this version or later.
- Is CVE-2026-77255 exploitable, and should I be worried? Whether CVE-2026-77255 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-2026-77255 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-2026-77255? Upgrade
mcp-atlassianto 0.22.0 or later.