CVE-2005-0173 in Squid
Summary
by MITRE
squid_ldap_auth in Squid 2.5 and earlier allows remote authenticated users to bypass username-based Access Control Lists (ACLs) via a username with a space at the beginning or end, which is ignored by the LDAP server.
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Analysis
by VulDB Data Team • 12/16/2024
The vulnerability described in CVE-2005-0173 affects Squid proxy server versions 2.5 and earlier, specifically within the squid_ldap_auth authentication module. This issue represents a classic input validation flaw that undermines the security controls designed to protect network resources through proper authentication and access control mechanisms. The vulnerability exploits a fundamental weakness in how Squid processes LDAP authentication responses, creating a potential bypass mechanism for authenticated users who possess maliciously crafted credentials.
The technical flaw stems from improper handling of whitespace characters in usernames received from LDAP servers during the authentication process. When Squid processes authentication requests through the squid_ldap_auth module, it fails to properly sanitize or validate username strings before applying access control rules. Specifically, usernames containing leading or trailing spaces are silently stripped by the LDAP server itself, yet Squid continues to process these stripped usernames for ACL evaluation. This discrepancy creates a scenario where an authenticated user can manipulate their username to include spaces at the beginning or end, effectively bypassing username-based ACL restrictions that were designed to prevent unauthorized access to network resources.
The operational impact of this vulnerability is significant for organizations relying on Squid as a proxy server with LDAP authentication and access control policies. Attackers who gain authenticated access to the proxy system can leverage this weakness to circumvent access restrictions that should prevent them from accessing specific resources or services. This bypass capability directly violates the principle of least privilege and could enable unauthorized users to access restricted content, corporate resources, or sensitive data that should only be available to specific user groups or roles. The vulnerability is particularly dangerous because it operates at the authentication boundary, where legitimate users are already authenticated but can still exploit this weakness to gain additional access privileges.
From a cybersecurity perspective, this vulnerability aligns with CWE-20, which describes "Improper Input Validation" and represents a common class of flaws that can lead to access control bypasses. The issue also relates to ATT&CK technique T1078.002, which covers "Valid Accounts: Domain Accounts," as it allows attackers to exploit legitimate authentication mechanisms to gain unauthorized access. Organizations using vulnerable Squid versions should immediately implement mitigations including upgrading to patched versions of Squid, implementing additional input sanitization measures, and reviewing access control policies to ensure they account for potential whitespace manipulation. The vulnerability demonstrates the critical importance of proper input validation at all layers of authentication systems and highlights the need for comprehensive security testing of authentication modules that interface with external identity providers.