CVE-2022-0711 in HAProxy
Summary
by MITRE • 03/03/2022
A flaw was found in the way HAProxy processed HTTP responses containing the "Set-Cookie2" header. This flaw could allow an attacker to send crafted HTTP response packets which lead to an infinite loop, eventually resulting in a denial of service condition. The highest threat from this vulnerability is availability.
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Analysis
by VulDB Data Team • 03/04/2022
The vulnerability identified as CVE-2022-0711 represents a critical flaw in HAProxy's HTTP response processing mechanism that specifically targets the handling of the "Set-Cookie2" header. This issue resides within the application layer of the network stack and demonstrates how seemingly innocuous HTTP header processing can lead to severe operational disruptions. The flaw manifests when HAProxy encounters HTTP responses containing the Set-Cookie2 header, which is an older HTTP cookie specification that has been largely superseded by the more modern Set-Cookie header but remains supported for backward compatibility. The vulnerability is classified under CWE-20, which encompasses improper input validation, specifically in how the proxy handles malformed or crafted cookie headers during response processing.
The technical exploitation of this vulnerability occurs through the manipulation of HTTP response packets that contain the Set-Cookie2 header in a manner designed to trigger an infinite loop within HAProxy's processing logic. When the proxy encounters such crafted responses, it enters a recursive processing state where it continuously handles the same cookie header information without proper termination conditions. This creates an unbounded loop that consumes system resources and ultimately leads to service exhaustion. The operational impact is particularly severe as it affects the availability of the proxy service, rendering it unable to process legitimate requests while consuming excessive CPU and memory resources. The vulnerability demonstrates how protocol handling flaws can be leveraged to create denial of service conditions that are difficult to detect and mitigate in real-time network environments.
From a cybersecurity perspective, this vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks through resource exhaustion. The flaw represents a classic example of how improper state management in network appliances can be exploited to create sustained service disruption. Organizations relying on HAProxy for load balancing and reverse proxy operations face significant risk as this vulnerability can be exploited remotely without authentication, making it particularly dangerous in production environments. The attack surface is broad as any HTTP response processed by HAProxy that contains the Set-Cookie2 header could potentially trigger the vulnerable code path, affecting web applications, APIs, and other services that depend on HAProxy for traffic management.
Mitigation strategies for CVE-2022-0711 should prioritize immediate patching of HAProxy installations to the latest versions that contain the fix for this specific vulnerability. Organizations should also implement network monitoring to detect unusual resource consumption patterns that may indicate exploitation attempts. Additional defensive measures include implementing rate limiting on HTTP response processing, configuring HAProxy to sanitize or reject Set-Cookie2 headers, and establishing automated alerting for abnormal processing behavior. Security teams should also consider implementing network segmentation to limit the impact of potential exploitation and ensure that HAProxy instances are regularly updated as part of their vulnerability management processes. The vulnerability underscores the importance of maintaining up-to-date network infrastructure and the need for thorough testing of security patches in production environments before deployment.