CVE-2026-8500: Web::Passwd for Perl RCE Vulnerability

CVE-2026-8500 Overview

CVE-2026-8500 is a command injection vulnerability in Web::Passwd versions through 0.03 for Perl. The module is a small Common Gateway Interface (CGI) application for managing htpasswd files using the Apache htpasswd command. The user parameter is neither validated nor escaped before being passed as the last argument on the command line. Attackers can inject shell metacharacters into this parameter to execute arbitrary operating system commands. This issue is categorized under CWE-78 (OS Command Injection) and results in remote code execution (RCE) on the host running the CGI application.

Critical Impact

Unauthenticated attackers reaching the CGI endpoint can inject shell commands via the user parameter, achieving remote code execution under the privileges of the web server process.

Affected Products

• Web::Passwd Perl module versions through 0.03
• CGI deployments exposing the Web::Passwd interface
• Web servers running the vulnerable module to manage htpasswd files

Discovery Timeline

• 2026-05-13 - Vulnerability disclosed on the Openwall OSS-Security mailing list
• 2026-05-13 - CVE-2026-8500 published to NVD
• 2026-05-14 - Last updated in NVD database

Technical Details for CVE-2026-8500

Vulnerability Analysis

Web::Passwd is a CGI wrapper around the Apache htpasswd utility, which administrators use to add, update, or remove entries in an htpasswd credential file. The application accepts user-controlled HTTP parameters and constructs a shell command line invoking htpasswd. The user parameter is appended as the final argument without sanitization, escaping, or validation. An attacker can supply shell metacharacters such as ;, |, backticks, or $() within the user value to break out of the intended argument context. The shell interprets the injected characters as additional commands, executing them with the privileges of the CGI process. The vulnerability requires no authentication when the CGI endpoint is exposed.

Root Cause

The root cause is missing input validation on the user parameter combined with insecure command construction. The module passes user input directly into a shell-interpreted command string rather than using a safe execution model such as a list-based system() invocation or parameterized API call. Per the MetaCPAN release page, version 0.03 is the latest published release of the module.

Attack Vector

An attacker submits a crafted HTTP request to the CGI script with a malicious user parameter value containing shell metacharacters. When the script builds the command line invoking htpasswd, the injected payload terminates the intended arguments and introduces attacker-controlled commands. The shell executes those commands with the permissions of the web server account, typically allowing file read and write, network egress, and further lateral movement. Refer to the Apache htpasswd documentation for context on how the underlying utility is invoked.

Detection Methods for CVE-2026-8500

Indicators of Compromise

• Web server access logs containing shell metacharacters (;, |, &, `, $() inside the user query string or form parameter
• Unexpected child processes of the web server such as sh, bash, nc, curl, wget, or perl spawning shortly after a request to the Web::Passwd CGI endpoint
• Modifications to htpasswd files or related configuration files outside scheduled change windows
• Outbound network connections originating from the CGI process to unfamiliar hosts

Detection Strategies

• Inspect CGI access logs for requests targeting the Web::Passwd script and parse the user parameter for shell metacharacters
• Correlate web requests with process creation events on the host to identify shell processes spawned by the CGI runtime
• Apply Web Application Firewall (WAF) rules that flag command injection payloads against the affected endpoint

Monitoring Recommendations

• Enable verbose CGI request logging and forward logs to a central analytics platform for retrospective hunting
• Monitor process trees on hosts running the module for htpasswd invocations followed by unrelated child processes
• Alert on filesystem changes to htpasswd files and on new executables written to web-accessible directories

How to Mitigate CVE-2026-8500

Immediate Actions Required

• Remove or disable the Web::Passwd CGI script from production web servers until a fixed version is available
• Restrict access to the CGI endpoint using network controls, authentication, or IP allowlisting
• Audit htpasswd files, web roots, and the CGI host for signs of unauthorized modification or command execution

Patch Information

No fixed version is listed at the time of publication. Version 0.03 is the most recent release on MetaCPAN. Administrators should track the Openwall advisory for updates and consider replacing the module with a maintained alternative that uses list-form process invocation.

Workarounds

• Place the CGI behind an authenticated reverse proxy and restrict access to trusted administrators only
• Deploy WAF signatures blocking shell metacharacters in the user parameter for the affected endpoint
• Replace the vulnerable script with a custom wrapper that calls htpasswd using Perl's list-form system(@args) or that updates the password file directly without invoking a shell

# Example: block the vulnerable endpoint at the web server until remediated
# Apache httpd configuration snippet
<Location "/cgi-bin/web-passwd">
    Require all denied
</Location>