CVE-2023-46846 is a critical security vulnerability identified in SQUID version 2.6, a widely used caching and forwarding HTTP proxy server. The vulnerability stems from an inconsistent interpretation of HTTP requests between SQUID and other HTTP intermediaries, specifically due to lenient handling of chunked transfer encoding during HTTP request parsing. This discrepancy enables HTTP request smuggling attacks, where an attacker crafts specially formed HTTP requests that are interpreted differently by the proxy and backend servers. By exploiting this, an attacker can bypass firewall rules and frontend security mechanisms, injecting unauthorized requests or responses into the communication stream. The vulnerability does not require any authentication or user interaction, making it remotely exploitable over the network. The CVSS v3.1 base score of 9.3 reflects its critical severity, with network attack vector, low attack complexity, no privileges required, no user interaction, and a scope change indicating that the vulnerability affects components beyond the initially vulnerable SQUID proxy. The impact on confidentiality is high, as attackers can potentially access or manipulate sensitive data by circumventing security controls. Integrity impact is low, and availability is not affected. Although no public exploits are currently known, the nature of HTTP request smuggling attacks and the critical score suggest a high risk of exploitation once weaponized. This vulnerability highlights the importance of consistent HTTP parsing and strict adherence to protocol specifications in proxy servers to prevent such attacks.

For European organizations, the impact of CVE-2023-46846 can be significant, especially for those relying on SQUID proxies for web caching, content filtering, or as reverse proxies in their network architecture. Successful exploitation can lead to unauthorized access to internal web applications, data leakage, and bypassing of security controls such as web application firewalls and intrusion detection systems. This can compromise sensitive corporate data, intellectual property, and personal data protected under GDPR, leading to regulatory penalties and reputational damage. The attack could also facilitate further lateral movement within networks, enabling attackers to escalate privileges or deploy additional payloads. Given the critical severity and ease of exploitation, organizations face a high risk if they do not promptly address the vulnerability. The lack of known exploits in the wild currently provides a window for proactive defense, but the threat landscape may evolve rapidly. The impact is particularly acute for sectors with high-value targets such as finance, government, telecommunications, and critical infrastructure providers across Europe.

To mitigate CVE-2023-46846, European organizations should take immediate and specific actions beyond generic patching advice: 1) Monitor vendor advisories and apply official patches or updates for SQUID as soon as they become available, prioritizing upgrade from version 2.6. 2) In the interim, configure SQUID to enforce strict HTTP request parsing by disabling lenient chunked decoding if possible, or apply custom filters to detect anomalous chunked requests. 3) Deploy or update web application firewalls (WAFs) and intrusion prevention systems (IPS) with signatures or heuristics designed to detect HTTP request smuggling patterns, including malformed chunked requests. 4) Conduct internal network traffic analysis to identify suspicious HTTP request patterns indicative of smuggling attempts. 5) Review and harden firewall and proxy configurations to limit exposure of SQUID services to untrusted networks, restricting access to trusted clients only. 6) Educate security teams about HTTP request smuggling techniques to improve detection and incident response capabilities. 7) Implement layered security controls, including strict input validation on backend servers, to reduce the impact of any smuggled requests that bypass the proxy. These targeted mitigations will reduce the attack surface and improve resilience against exploitation.