Source: cve@mitre.org
The G/PGP (GPG) Plugin 2.1 and earlier for Squirrelmail allow remote authenticated users to execute arbitrary commands via shell metacharacters in (1) the fpr parameter to the deleteKey function in gpg_keyring.php, as called by (a) import_key_file.php, (b) import_key_text.php, and (c) keyring_main.php; and (2) the keyserver parameter to the gpg_recv_key function in gpg_key_functions.php, as called by gpg_options.php. NOTE: this issue may overlap CVE-2007-3636.
Squirrelmail's GPG plugin is vulnerable to remote command execution, allowing authenticated attackers to inject and execute arbitrary commands on the server. This vulnerability stems from improper sanitization of user-supplied input, specifically within the plugin's handling of GPG key management functions. Successful exploitation can lead to complete system compromise.
Step 1: Authentication: The attacker must first authenticate to the Squirrelmail webmail interface, gaining access to the GPG plugin functionality.
Step 2: Payload Injection (fpr parameter): The attacker crafts a malicious fpr value containing shell metacharacters (e.g., ;, &, |, $(...)). This payload is sent to the deleteKey function via import_key_file.php, import_key_text.php, or keyring_main.php.
Step 3: Payload Injection (keyserver parameter): The attacker crafts a malicious keyserver value containing shell metacharacters. This payload is sent to the gpg_recv_key function via gpg_options.php.
Step 4: Command Execution: The plugin constructs a shell command using the attacker-controlled input. The shell metacharacters in the payload are interpreted by the shell, allowing the attacker to execute arbitrary commands on the server.
Step 5: Privilege Escalation (if applicable): Depending on the server configuration and the attacker's goals, further actions may be taken to escalate privileges or maintain persistence.
The vulnerability arises from a lack of input validation and sanitization within the GPG plugin for Squirrelmail. Specifically, the plugin fails to properly sanitize user-supplied input passed to system calls related to GPG key management. The fpr parameter in the deleteKey function of gpg_keyring.php and the keyserver parameter in the gpg_recv_key function of gpg_key_functions.php are vulnerable. These parameters are used to construct shell commands without proper escaping or filtering of shell metacharacters. This allows an attacker to inject malicious commands, which are then executed by the underlying operating system. The root cause is a command injection vulnerability due to insufficient input validation. The plugin trusts user-supplied data, leading to the execution of arbitrary commands. The use of system() or similar functions without proper sanitization is the primary flaw.
While no specific APTs are directly linked to this CVE, the nature of the vulnerability (remote command execution) makes it attractive to various threat actors. This type of vulnerability is often used by attackers to gain initial access and establish a foothold. This CVE is not listed in CISA KEV.
Monitor web server logs (e.g., Apache, Nginx) for suspicious POST requests to gpg_keyring.php, import_key_file.php, import_key_text.php, keyring_main.php, or gpg_options.php with unusual fpr or keyserver parameter values containing shell metacharacters.
Analyze web server access logs for unusual command executions or file modifications initiated by the web server user.
Implement file integrity monitoring to detect unauthorized changes to critical system files.
Network Intrusion Detection Systems (IDS) can be configured to detect malicious payloads containing shell metacharacters in HTTP requests.
Review Squirrelmail and plugin logs for error messages or suspicious activity related to GPG key management.
Upgrade to the latest version of Squirrelmail and the GPG plugin, if available, or a version where the vulnerability is patched. (Note: This is an old CVE and may not have official patches.)
Implement input validation and sanitization for all user-supplied input, especially parameters used in system calls. Specifically, escape or filter shell metacharacters before passing them to the system() or similar functions.
Use a more secure method for executing external commands, such as using the escapeshellarg() and escapeshellcmd() functions in PHP to properly escape user-supplied input.
Restrict the permissions of the web server user to the minimum necessary to perform its tasks. This limits the impact of a successful exploit.
Regularly update and patch the underlying operating system and all installed software.
Consider disabling the GPG plugin if it is not required for business operations.