CVE-2010-1637 in SquirrelMail
Summary
by MITRE
The Mail Fetch plugin in SquirrelMail 1.4.20 and earlier allows remote authenticated users to bypass firewall restrictions and use SquirrelMail as a proxy to scan internal networks via a modified POP3 port number.
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Analysis
by VulDB Data Team • 09/18/2021
The vulnerability described in CVE-2010-1637 represents a significant security flaw within the Mail Fetch plugin of SquirrelMail versions 1.4.20 and earlier. This issue stems from improper input validation and access control mechanisms that allow authenticated users to manipulate network connections through the email client's proxy functionality. The vulnerability specifically targets the plugin's handling of POP3 port numbers, creating an avenue for malicious actors to leverage the email system as an unauthorized network scanning tool.
The technical implementation of this vulnerability resides in the plugin's failure to properly validate and sanitize user-supplied port numbers during the mail fetching process. When users authenticate to SquirrelMail and attempt to fetch mail from remote servers, the Mail Fetch plugin accepts modified port specifications without adequate verification. This lack of input sanitization creates a path where authenticated users can specify arbitrary port numbers, effectively enabling them to redirect network traffic through the SquirrelMail server. The flaw operates under CWE-20, which catalogs improper input validation as a fundamental weakness in software security architecture.
The operational impact of this vulnerability extends beyond simple network scanning capabilities, creating a potential vector for broader reconnaissance activities within internal network environments. An attacker with valid credentials can utilize the compromised SquirrelMail instance to perform port scanning operations against internal systems that would normally be protected by firewalls. This proxy functionality essentially allows the attacker to use the email server as a pivot point for network enumeration, potentially identifying open ports, services, and network topology elements that should remain hidden from external access. The vulnerability undermines the fundamental security boundary that firewalls establish between internal and external networks.
The implications of this vulnerability align with several tactics described in the MITRE ATT&CK framework, particularly those related to network discovery and lateral movement. Attackers can leverage this proxy functionality to map internal network structures without direct access to the network infrastructure, effectively bypassing traditional network security controls. The vulnerability also demonstrates how web-based applications can inadvertently become attack vectors when proper access controls and input validation mechanisms are absent. Organizations relying on SquirrelMail for email services face increased risk of internal network reconnaissance and potential subsequent exploitation of discovered services.
Mitigation strategies for this vulnerability should focus on immediate patching of affected SquirrelMail versions, implementing strict input validation for all network-related parameters, and establishing network-level controls to prevent unauthorized proxy usage. Organizations should also consider implementing additional authentication layers, monitoring for unusual network activity patterns, and conducting regular security assessments of web-based email solutions. The remediation process must include thorough testing of patched implementations to ensure that legitimate functionality remains intact while preventing the exploitation vector described in CVE-2010-1637.