CVE-2023-25950 in HAProxy
Summary
by MITRE • 04/11/2023
HTTP request/response smuggling vulnerability in HAProxy version 2.7.0, and 2.6.1 to 2.6.7 allows a remote attacker to alter a legitimate user's request. As a result, the attacker may obtain sensitive information or cause a denial-of-service (DoS) condition.
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Analysis
by VulDB Data Team • 11/03/2025
The HTTP request/response smuggling vulnerability identified as CVE-2023-25950 affects HAProxy versions 2.7.0 and 2.6.1 through 2.6.7, representing a critical security flaw that enables remote attackers to manipulate legitimate user requests. This vulnerability stems from improper handling of HTTP message boundaries and header parsing within the load balancing and proxying mechanisms of HAProxy, creating opportunities for attackers to inject malicious content or alter request flows. The flaw specifically impacts the HTTP protocol interpretation logic that processes incoming requests and outgoing responses, allowing adversaries to exploit inconsistencies between how different components of the proxy handle HTTP messages.
The technical implementation of this vulnerability involves manipulation of HTTP headers and message framing that leads to inconsistent interpretation of request boundaries by the backend servers. Attackers can craft malicious requests that appear legitimate to the HAProxy frontend but are interpreted differently by the backend systems, potentially enabling data leakage, session hijacking, or service disruption. This type of vulnerability falls under CWE-444, which specifically addresses HTTP response splitting and related smuggling techniques, and aligns with ATT&CK technique T1190 for exploitation of vulnerabilities in network infrastructure components. The flaw exploits the fundamental HTTP protocol parsing mechanisms that HAProxy uses to forward requests, creating a mismatch between what the proxy expects to receive and what it actually processes.
The operational impact of CVE-2023-25950 extends beyond simple information disclosure, as it can enable sophisticated attacks including cache poisoning, cross-site scripting exploitation, and authentication bypass attempts. Remote attackers can leverage this vulnerability to perform unauthorized actions against backend services, potentially leading to complete system compromise if the backend applications are not properly secured. The vulnerability creates a persistent threat vector that remains active as long as affected HAProxy versions are deployed in production environments, making it particularly dangerous for organizations with extensive load balancing infrastructure. Organizations may experience service degradation, data breaches, or complete denial-of-service conditions when this vulnerability is exploited.
Mitigation strategies for CVE-2023-25950 require immediate deployment of patched HAProxy versions, specifically versions 2.7.1 and 2.6.8, which contain the necessary fixes for the HTTP parsing inconsistencies. Organizations should also implement network segmentation and monitoring to detect anomalous HTTP traffic patterns that might indicate exploitation attempts. Additional defensive measures include enabling strict HTTP header validation, implementing rate limiting, and deploying web application firewalls to filter suspicious requests. Security teams should conduct comprehensive vulnerability assessments of their entire proxy infrastructure and establish incident response procedures specifically addressing HTTP smuggling attacks. The remediation process must include thorough testing of patched configurations to ensure that the fixes do not introduce performance regressions or compatibility issues with existing applications.