CVE-2012-2213 in Squid
Summary
by MITRE
** DISPUTED ** Squid 3.1.9 allows remote attackers to bypass the access configuration for the CONNECT method by providing an arbitrary allowed hostname in the Host HTTP header. NOTE: this issue might not be reproducible, because the researcher is unable to provide a squid.conf file for a vulnerable system, and the observed behavior is consistent with a squid.conf file that was (perhaps inadvertently) designed to allow access based on a "req_header Host" acl regex that matches www.uol.com.br.
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Analysis
by VulDB Data Team • 08/06/2024
The vulnerability described in CVE-2012-2213 represents a significant access control flaw in Squid proxy server version 3.1.9 that could potentially allow remote attackers to circumvent configured security policies. This issue specifically targets the CONNECT method handling within the proxy server's configuration system, creating a potential pathway for unauthorized network access that undermines the intended security boundaries of the proxy infrastructure.
The technical flaw manifests when Squid processes HTTP CONNECT requests where an attacker can manipulate the Host header to include an arbitrary hostname that is permitted by the access control lists. This vulnerability falls under the category of improper access control as defined by CWE-284, where the proxy server fails to properly validate or enforce access restrictions during secure tunnel establishment. The vulnerability is particularly concerning because it affects the CONNECT method which is commonly used for HTTPS traffic and secure communications, making it a critical vector for bypassing network security controls.
The operational impact of this vulnerability extends beyond simple access bypass to potentially compromise the entire proxy security model. When an attacker successfully exploits this flaw, they can establish connections to hosts that should be restricted or blocked by the proxy configuration, effectively creating unauthorized access paths through the network infrastructure. This could result in data exfiltration, unauthorized access to internal resources, or the ability to bypass corporate security policies designed to protect against malicious traffic. The vulnerability's potential to allow access to restricted domains through manipulated Host headers creates a persistent security risk that could remain undetected for extended periods.
The reported inconsistency in reproducibility highlights the complexity of this vulnerability and its dependence on specific Squid configuration parameters. The issue may be related to how certain access control list configurations interact with the Host header processing, particularly when using req_header Host ACL regex patterns. This suggests that the vulnerability is not universal but rather depends on specific configuration patterns where the Host header validation does not properly integrate with the overall access control framework. Organizations should carefully review their Squid configuration files to identify potential exposure and ensure that access control lists are properly implemented to prevent such header-based bypasses. The vulnerability aligns with ATT&CK technique T1071.004 for application layer protocol tunneling, where proxy servers are used to establish unauthorized connections through legitimate network access points.
Mitigation strategies should focus on implementing comprehensive access control validation that properly validates all request headers against configured policies, particularly for CONNECT method requests. Organizations should update to patched versions of Squid where available, and implement additional monitoring to detect unusual CONNECT request patterns. The configuration should be reviewed to ensure that Host header ACLs are properly enforced and that there are no conflicting rules that could allow bypass. Network segmentation and additional firewall rules should complement proxy security measures to provide defense in depth. Regular security audits of proxy configurations should be conducted to identify potential misconfigurations that could enable similar bypass techniques. The vulnerability underscores the importance of thorough testing and validation of proxy configurations, particularly in environments where strict access controls are required to maintain network security boundaries.