Executive Summary

CVE-2026-4631 is a critical vulnerability in Cockpit, a web-based server management tool for Linux. The issue arises because Cockpit's remote login feature passes user-supplied hostnames and usernames directly to the SSH client without any validation or sanitization.

An attacker with network access to the Cockpit web service can send a specially crafted HTTP request to the login endpoint that injects malicious SSH options or shell commands. This injection happens before any credential verification, meaning the attacker does not need valid login credentials to exploit it.

The vulnerability allows remote code execution on the Cockpit host by exploiting how SSH command-line arguments are constructed and executed. Specifically, the username and hostname parameters are passed as command-line arguments to the SSH client without checks, enabling injection of commands or SSH options.

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Impact Analysis

This vulnerability can have severe impacts because it allows unauthenticated remote code execution on the Cockpit host. An attacker can execute arbitrary commands on the server running Cockpit without needing any valid credentials.

• Complete compromise of the Cockpit host system.
• Potential unauthorized access to sensitive data or system resources.
• Disruption of server management operations.
• Possibility for attackers to establish persistent access or pivot to other systems.

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Detection Guidance

Detection of this vulnerability involves monitoring for unusual or crafted HTTP requests to the Cockpit web service, specifically targeting the login endpoint with suspicious username or hostname parameters that may contain shell metacharacters or SSH options.

Since the exploit is triggered by a single HTTP request to the endpoint `/cockpit+=<hostname>/login` with an Authorization header, network detection can focus on identifying such requests with unusual or malformed parameters.

On the system, checking the version of Cockpit and OpenSSH can help determine vulnerability status: Cockpit versions >= 326/327 combined with OpenSSH versions older than 9.6 are vulnerable.

• Use network monitoring tools (e.g., tcpdump, Wireshark) to capture HTTP requests to the Cockpit service and filter for requests to the login endpoint containing suspicious characters.
• Check Cockpit version: `rpm -q cockpit` or equivalent package manager commands.
• Check OpenSSH version: `ssh -V` to ensure it is version 9.6 or newer.
• Review system logs for unexpected SSH command executions or unusual file creations (e.g., presence of files like `/tmp/flag` as in the example exploit).

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Mitigation Strategies

Immediate mitigation steps include updating affected components and applying configuration changes to prevent exploitation.

• Upgrade OpenSSH to version 9.6 or later, which includes early hostname validation rejecting hostnames and usernames with shell metacharacters.
• Upgrade Cockpit to version 327 or later, where fixes such as inserting a `--` separator before the hostname argument and input validation are implemented.
• If immediate upgrades are not possible, restrict network access to the Cockpit web service to trusted users only, minimizing exposure.
• Implement firewall rules or network segmentation to block unauthorized access to the Cockpit login endpoint.
• Monitor logs and network traffic for suspicious activity targeting the Cockpit login endpoint.

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Compliance Impact

The provided information does not specify how CVE-2026-4631 affects compliance with common standards and regulations such as GDPR or HIPAA.

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