CVE-2025-47203: Dropbear SSH Command Injection Vulnerability

CVE-2025-47203 Overview

CVE-2025-47203 is a command injection vulnerability in the dbclient component of Dropbear SSH versions prior to 2025.88. The vulnerability exists because the application uses a shell to process hostname arguments without proper sanitization, allowing attackers to inject arbitrary commands through specially crafted, untrusted hostname values.

Critical Impact

Attackers can execute arbitrary commands on systems running vulnerable versions of Dropbear SSH's dbclient by supplying maliciously crafted hostname arguments that exploit the shell invocation mechanism.

Affected Products

• Dropbear SSH versions before 2025.88
• Systems using dbclient with untrusted hostname inputs
• Embedded devices and IoT systems commonly running Dropbear SSH

Discovery Timeline

• May 7, 2025 - CVE-2025-47203 published to NVD
• May 17, 2025 - Last updated in NVD database

Technical Details for CVE-2025-47203

Vulnerability Analysis

This command injection vulnerability (CWE-78) affects the dbclient binary, which is the SSH client component of Dropbear SSH. The core issue stems from how the application handles hostname arguments when establishing SSH connections. When processing the hostname parameter, dbclient passes the value through a shell without adequate input validation or sanitization.

The vulnerability requires local access and has a changed scope, meaning successful exploitation can impact resources beyond the vulnerable component's security scope. While the attack complexity is high due to the specific conditions required, no privileges or user interaction are needed to exploit the vulnerability once an attacker can influence the hostname argument.

Root Cause

The root cause of CVE-2025-47203 lies in the use of shell invocation when processing hostname arguments in dbclient. The vulnerable code path in cli-main.c passes user-supplied hostname data to a shell without proper escaping or validation. This design flaw allows shell metacharacters embedded in hostname strings to be interpreted as commands rather than literal text.

When the hostname argument contains shell metacharacters such as backticks, semicolons, or command substitution syntax, these characters are processed by the shell, leading to command execution in the context of the user running dbclient.

Attack Vector

The attack requires local access to a system where an attacker can influence the hostname argument passed to dbclient. This commonly occurs in scenarios where:

• Scripts or automation tools construct SSH connection strings using external or user-controlled input
• Configuration management systems pass untrusted hostnames to Dropbear's SSH client
• Applications integrate dbclient and accept hostname parameters from untrusted sources

An attacker crafts a malicious hostname containing shell metacharacters and command payloads. When this hostname is processed by dbclient, the shell interprets the embedded commands, resulting in arbitrary command execution. The impact includes potential confidentiality and integrity breaches, as indicated by the vulnerability's ability to affect resources beyond the vulnerable component's scope.

Detection Methods for CVE-2025-47203

Indicators of Compromise

• Unusual command execution patterns originating from dbclient processes
• Shell metacharacters appearing in SSH connection logs or command history
• Unexpected child processes spawned by dbclient instances
• Anomalous network connections or file system modifications traced to SSH client activity

Detection Strategies

• Monitor dbclient process execution with arguments containing shell metacharacters such as ;, |, $(), or backticks
• Implement process tree analysis to detect unexpected command execution spawned from dbclient
• Deploy file integrity monitoring on systems running Dropbear SSH to detect unauthorized modifications
• Enable comprehensive logging for SSH client invocations and analyze for injection patterns

Monitoring Recommendations

• Configure audit rules to log all dbclient executions and their command-line arguments
• Implement behavioral analysis for SSH client processes to detect anomalous activity
• Review scripts and automation that invoke dbclient for proper input validation
• Monitor for exploitation attempts by analyzing process creation events and command-line arguments

How to Mitigate CVE-2025-47203

Immediate Actions Required

• Upgrade Dropbear SSH to version 2025.88 or later immediately
• Audit all scripts and applications that invoke dbclient with external or user-supplied hostnames
• Implement strict input validation for any hostname parameters passed to SSH clients
• Consider using allowlists for permitted hostnames in automated SSH connections

Patch Information

The vulnerability has been addressed in Dropbear SSH version 2025.88. The fix involves properly handling hostname arguments to prevent shell interpretation of metacharacters. Security patches and details are available through the GitHub Change Log and the source code repository. Debian users should refer to the Debian LTS Announcement for distribution-specific updates.

Workarounds

• Validate and sanitize all hostname inputs before passing them to dbclient
• Use allowlists to restrict hostnames to known, trusted values only
• Wrap dbclient invocations with input validation scripts that reject shell metacharacters
• Consider switching to alternative SSH clients until patching is complete

# Example input validation wrapper for dbclient
#!/bin/bash
# Validate hostname to prevent command injection
HOSTNAME="$1"
# Reject hostnames containing shell metacharacters
if [[ "$HOSTNAME" =~ [;\|\`\$\(\)\{\}\<\>\&] ]]; then
    echo "Error: Invalid characters in hostname" >&2
    exit 1
fi
# Proceed with validated hostname
/usr/bin/dbclient "$HOSTNAME" "${@:2}"