A critical security vulnerability in Apache Traffic Server (ATS)<\/a> has been discovered. By exploiting how the server processes chunked messages, attackers can perform request smuggling attacks.\u00a0<\/p>\n The vulnerability, tracked as CVE-2024-53868, affects multiple versions of this high-performance HTTP proxy server and requires system administrators\u2019 immediate attention.<\/p>\n According to the advisory, the vulnerability stems from a flaw in how Apache Traffic Server handles HTTP chunked transfer encoding\u2014a method that allows data to be sent in a series of chunks rather than all at once.\u00a0<\/p>\n When processing malformed chunked messages, ATS fails to properly validate the message format, creating a security gap that malicious actors can exploit.<\/p>\n Specifically, the issue involves how ATS handles malformed chunked message bodies. Based on findings from related GitHub<\/a> issues, ATS improperly accepts and forwards requests containing invalid formatting elements, such as carriage returns within chunk-ext whitespace, where only spaces and tabs should be permitted.<\/p>\n Additionally, ATS accepts bare Line Feed (LF) characters as line endings within chunked message bodies instead of requiring the standard Carriage Return + Line Feed (CRLF) sequence.<\/p>\n For example, when a specially crafted HTTP request using the Transfer-Encoding: chunked header with intentionally malformed chunk formatting is sent to an ATS server, the server processes it in a way that differs from how backend servers might interpret the same request.\u00a0<\/p>\n This inconsistency creates the opportunity for request smuggling.<\/p>\n The above-simplified example demonstrates how an improper line ending (bare LF represented as n) in a chunked message might be accepted by ATS and forwarded to backend servers without proper normalization.<\/p>\n The summary of the vulnerability is given below:<\/p>\nApache Traffic Server Vulnerability<\/strong><\/h2>\n
![\"\"](\"https:\/\/lh7-rt.googleusercontent.com\/docsz\/AD_4nXfPDDvmijtp0CWw_-9-NuF3l0v_dtZxIbDA5_z2woSipEIJZZopjLyGW5nnCl99x24A5O2g5sIFdqflXJfD8RxAGGKIm4aysDEo0TDT74LD5nE57Terlx5v0JrwYzLg_J1afrkEnA?key=5Op9TrRT1fX175I8ziHhKzDi\")