CVE-2024-23452 is a high-severity HTTP request smuggling vulnerability affecting Apache bRPC versions 0.9.5 through 1.7.0 on all platforms. The root cause lies in the http_parser component of Apache bRPC, which does not fully comply with the RFC-7230 HTTP/1.1 specification. Specifically, the parser mishandles HTTP requests that contain both Transfer-Encoding (TE) and Content-Length headers. According to RFC-7230, such requests should be treated carefully to avoid ambiguity in message framing. However, Apache bRPC's parser incorrectly processes these headers, allowing an attacker to smuggle malicious HTTP requests through a persistent connection between a frontend server and the backend bRPC HTTP server. In this attack scenario, the frontend server parses requests using the TE header, expecting chunked encoding, while the backend server interprets the request differently, enabling the attacker to inject a hidden request. This can lead to request smuggling or response splitting attacks, which can be leveraged to bypass security controls, poison caches, hijack user sessions, or conduct cross-site scripting and other injection attacks. The vulnerability requires no authentication or user interaction and can be exploited remotely over the network. The Apache Software Foundation has addressed this issue in bRPC version 1.8.0, and a patch is available. The CVSS v3.1 base score is 7.5 (high), reflecting the network attack vector, low attack complexity, no privileges required, no user interaction, unchanged scope, no confidentiality impact, but high integrity impact and no availability impact.

For European organizations, this vulnerability poses a significant risk, especially for those using Apache bRPC in their backend infrastructure. The ability to smuggle HTTP requests can allow attackers to bypass security mechanisms such as web application firewalls, load balancers, or reverse proxies, potentially leading to unauthorized actions, data manipulation, or session hijacking. This can compromise the integrity of web applications and services, leading to data corruption or unauthorized transactions. Given that Apache bRPC is used in distributed systems and microservices architectures, exploitation could affect critical internal communications, impacting business operations. The lack of confidentiality impact reduces the risk of direct data leakage, but the high integrity impact means attackers can alter data or commands, which can have severe consequences in sectors like finance, healthcare, or government services prevalent in Europe. Additionally, the vulnerability's remote exploitability without authentication increases the attack surface, making it attractive for threat actors targeting European enterprises. Although no known exploits are currently reported in the wild, proactive mitigation is essential to prevent potential attacks.

European organizations should prioritize upgrading Apache bRPC to version 1.8.0, which contains the official fix for this vulnerability. If immediate upgrading is not feasible, applying the official patch from the Apache bRPC GitHub repository (pull request #2518) is critical. Network administrators should review and harden frontend and backend HTTP server configurations to ensure strict compliance with RFC-7230, particularly regarding handling of Transfer-Encoding and Content-Length headers. Deploying web application firewalls (WAFs) with rules specifically designed to detect and block HTTP request smuggling attempts can provide an additional layer of defense. Monitoring persistent HTTP connections for anomalous or unexpected header combinations can help detect exploitation attempts. Organizations should also conduct internal code reviews and penetration testing focusing on HTTP request parsing logic in their infrastructure. Finally, maintaining an up-to-date inventory of Apache bRPC deployments and ensuring timely patch management processes will reduce exposure.