The vulnerability identified as CVE-2024-49214 affects the QUIC protocol implementation in HAProxy versions 2.9.x prior to 2.9.11, 3.0.x prior to 3.0.5, and 3.1.x prior to 3.1-dev7. QUIC is a transport layer network protocol designed to improve performance and security for web traffic. In this case, the flaw allows an attacker to initiate a 0-RTT (zero round-trip time) session using a spoofed IP address. Normally, HAProxy uses IP allow/block lists as a security control to restrict or permit traffic based on source IP addresses. However, due to this vulnerability, the IP address verification can be bypassed during the 0-RTT session establishment phase, allowing unauthorized connections that should have been blocked. This issue arises because the 0-RTT mechanism accepts early data before full handshake completion, and the implementation does not properly validate the source IP against the configured access control lists at this stage. The vulnerability is classified under CWE-290 (Authentication Bypass by Spoofing) and does not require any privileges or user interaction to exploit. Although no active exploitation has been reported, the flaw poses a risk to environments relying on IP-based filtering for security. The CVSS v3.1 base score is 5.3, indicating a medium severity level, with the vector highlighting low attack complexity, network attack vector, no privileges required, no user interaction, and impact limited to integrity (bypassing access control).

This vulnerability can undermine the effectiveness of IP allow/block lists, a common security control used to restrict access to sensitive services or networks. By bypassing these controls, attackers can gain unauthorized access to backend systems or services protected by HAProxy, potentially leading to unauthorized data manipulation or lateral movement within the network. Although confidentiality and availability are not directly impacted, the integrity of access control is compromised, which can facilitate further attacks or unauthorized activities. Organizations that rely heavily on IP-based filtering for perimeter defense or internal segmentation are particularly at risk. The ease of exploitation without authentication or user interaction increases the threat level, especially in environments exposed to untrusted networks. The lack of known exploits in the wild suggests limited current impact, but the vulnerability should be addressed promptly to prevent future abuse. Failure to mitigate this issue could lead to compliance violations and increased risk of breach in regulated industries.

1. Upgrade HAProxy to the latest patched versions: 2.9.11 or later, 3.0.5 or later, and 3.1-dev7 or later where this vulnerability is fixed. 2. If immediate patching is not feasible, consider disabling QUIC support in HAProxy to eliminate the attack vector related to 0-RTT sessions. 3. Implement additional layers of access control beyond IP filtering, such as mutual TLS authentication or application-layer authentication, to reduce reliance on IP-based controls. 4. Monitor HAProxy logs for unusual 0-RTT session attempts or unexpected source IP addresses to detect potential exploitation attempts. 5. Employ network-level protections like firewall rules or intrusion detection systems to restrict traffic to trusted sources and detect spoofing attempts. 6. Review and tighten IP allow/block list configurations to ensure they are as restrictive as possible. 7. Conduct regular security assessments and penetration testing focusing on HAProxy configurations and QUIC protocol usage to identify residual risks.