CVE-2007-3778 in GPG Plugin
Summary
by MITRE
The G/PGP (GPG) Plugin 2.0, and 2.1dev before 20060912, for Squirrelmail allows remote attackers to execute arbitrary commands via shell metacharacters in the messageSignedText parameter to the gpg_check_sign_pgp_mime function in gpg_hook_functions.php. NOTE: a parameter value can be set in the contents of an e-mail message.
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Analysis
by VulDB Data Team • 07/21/2021
The vulnerability described in CVE-2007-3778 represents a critical command injection flaw within the GPG plugin for Squirrelmail email client. This security weakness affects versions 2.0 and 2.1dev prior to the 20060912 release, creating a significant attack surface for remote threat actors seeking to compromise email systems. The vulnerability specifically resides in the gpg_check_sign_pgp_mime function located within the gpg_hook_functions.php file, where insufficient input validation allows malicious actors to inject shell metacharacters that can be executed with the privileges of the web server process. The attack vector is particularly concerning because it leverages email message contents as the attack payload, making it difficult to detect and prevent through traditional network security measures.
The technical implementation of this vulnerability stems from improper sanitization of user-supplied data within the email message body. When Squirrelmail processes signed PGP/MIME messages through the vulnerable GPG plugin, the messageSignedText parameter is directly incorporated into shell commands without adequate filtering or escaping of special characters. This design flaw aligns with CWE-77, which describes improper neutralization of special elements used in a command, and CWE-94, which addresses the execution of arbitrary code due to insufficient input validation. The vulnerability essentially allows attackers to craft specially formatted email messages that contain shell metacharacters such as semicolons, ampersands, or backticks that get executed when the plugin processes the signed message content.
The operational impact of this vulnerability extends beyond simple command execution, as it provides attackers with potential access to the underlying system hosting the Squirrelmail instance. Depending on the web server configuration and privileges granted to the Squirrelmail process, successful exploitation could lead to complete system compromise, data exfiltration, or further lateral movement within the network. The fact that the attack requires no authentication or special privileges makes this vulnerability particularly dangerous in environments where email systems are accessible to external users or where internal email traffic is not properly segmented. This weakness directly maps to ATT&CK technique T1059, which covers command and scripting interpreter, and T1078, which addresses valid accounts, as the compromised system may be used for further malicious activities.
Organizations affected by this vulnerability should immediately implement mitigations including updating to patched versions of the GPG plugin for Squirrelmail, implementing proper input validation and sanitization for email content, and establishing network segmentation to limit access to email systems. The recommended approach involves deploying web application firewalls to detect and block malicious shell metacharacters in email processing, implementing strict content filtering for PGP/MIME messages, and ensuring that the web server runs with minimal required privileges. Additionally, administrators should conduct thorough security audits of all email plugins and components to identify similar vulnerabilities and establish monitoring procedures to detect potential exploitation attempts. The vulnerability highlights the importance of secure coding practices and input validation in web applications, particularly those handling user-generated content, and serves as a reminder of the critical need for regular security updates and vulnerability assessments in email infrastructure.