CVE-2024-35161 in Traffic Server
Summary
by MITRE • 07/26/2024
Apache Traffic Server forwards malformed HTTP chunked trailer section to origin servers. This can be utilized for request smuggling and may also lead cache poisoning if the origin servers are vulnerable.
This issue affects Apache Traffic Server: from 8.0.0 through 8.1.10, from 9.0.0 through 9.2.4.
Users can set a new setting (proxy.config.http.drop_chunked_trailers) not to forward chunked trailer section. Users are recommended to upgrade to version 8.1.11 or 9.2.5, which fixes the issue.
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Analysis
by VulDB Data Team • 09/28/2024
Apache Traffic Server version 8.0.0 through 8.1.10 and 9.0.0 through 9.2.4 contains a critical vulnerability in its HTTP handling mechanism that allows attackers to exploit malformed chunked transfer encoding trailers. This vulnerability stems from the server's improper validation and forwarding of HTTP chunked encoding trailer sections to origin servers. The flaw manifests when the proxy receives HTTP requests with malformed chunked trailers that do not conform to RFC 7230 standards for transfer encoding. These malformed trailers contain additional header fields that are not properly sanitized or validated before being forwarded to backend servers, creating a potential attack vector for HTTP request smuggling techniques.
The technical implementation of this vulnerability occurs at the HTTP protocol parsing layer where Apache Traffic Server processes chunked transfer encoding. When a client sends a request with chunked encoding containing malformed trailers, the proxy server fails to properly validate these trailer sections against established HTTP standards. The server then forwards these malformed trailers to origin servers without sufficient sanitization, allowing attackers to manipulate the HTTP request flow. This behavior aligns with CWE-119, which addresses improper restriction of operations within a defined access scope, and represents a failure in input validation and sanitization processes. The vulnerability specifically targets the HTTP chunked transfer encoding implementation as defined in RFC 7230, where trailer sections contain optional header fields that must be properly handled.
The operational impact of this vulnerability extends beyond simple request forwarding and creates significant security implications for organizations using Apache Traffic Server as a reverse proxy or cache. Attackers can leverage this weakness to perform HTTP request smuggling attacks by crafting malicious chunked requests that manipulate how requests are processed by both the proxy and origin servers. This technique allows attackers to potentially bypass security controls, access restricted resources, or perform unauthorized operations by exploiting inconsistencies in how different servers handle the malformed trailer sections. The vulnerability also introduces cache poisoning risks when origin servers are themselves vulnerable to malformed HTTP requests, as the forwarded trailers can contain data that corrupts cache entries or influences cache behavior. This aligns with ATT&CK technique T1590, which covers reconnaissance techniques for identifying application vulnerabilities, and T1190, which involves exploiting vulnerabilities in web applications through malformed requests.
Organizations affected by this vulnerability should immediately implement the recommended mitigation strategies including enabling the new configuration parameter proxy.config.http.drop_chunked_trailers to prevent forwarding of chunked trailer sections. This configuration setting effectively disables the problematic behavior by dropping trailer sections entirely, preventing attackers from exploiting the vulnerability. The most effective long-term solution involves upgrading to Apache Traffic Server versions 8.1.11 or 9.2.5, which contain patches specifically addressing the malformed trailer handling issue. These patched versions implement proper validation of chunked transfer encoding trailers and ensure compliance with RFC 7230 standards. Security teams should also conduct thorough network monitoring to detect any potential exploitation attempts and implement additional security controls such as web application firewalls to provide defense-in-depth protection against similar vulnerabilities in the HTTP protocol stack.