CVE-2021-37147 in Traffic Server
Summary
by MITRE • 11/03/2021
Improper input validation vulnerability in header parsing of Apache Traffic Server allows an attacker to smuggle requests. This issue affects Apache Traffic Server 8.0.0 to 8.1.2 and 9.0.0 to 9.1.0.
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Analysis
by VulDB Data Team • 06/10/2024
The vulnerability identified as CVE-2021-37147 represents a critical flaw in Apache Traffic Server's HTTP header parsing mechanism that enables HTTP request smuggling attacks. This issue resides in the improper validation of input data within the server's header processing pipeline, creating a pathway for malicious actors to manipulate HTTP request flows. The vulnerability specifically impacts versions 8.0.0 through 8.1.2 and 9.0.0 through 9.1.0 of the Apache Traffic Server software, making it a widespread concern across multiple release lines of this popular web proxy and cache server implementation.
The technical root cause of this vulnerability stems from insufficient validation of HTTP header fields during the request parsing phase. When Apache Traffic Server processes incoming HTTP requests, it fails to properly validate the structure and content of header fields, allowing attackers to craft malformed headers that can be interpreted differently by the server and subsequent backend systems. This parsing inconsistency creates opportunities for request smuggling where an attacker can inject or manipulate headers in ways that cause the server to forward different requests to backend services than what the client originally intended. The flaw operates at the application layer and leverages the inherent complexity of HTTP protocol handling, particularly when dealing with header field normalization and parsing edge cases.
The operational impact of CVE-2021-37147 extends beyond simple data manipulation, as it can enable sophisticated attack vectors including cache poisoning, session hijacking, and cross-site request forgery exploitation. Attackers can leverage this vulnerability to bypass security controls, access restricted resources, or manipulate application behavior by smuggling requests through the proxy server. The vulnerability particularly affects environments where Apache Traffic Server acts as a reverse proxy or forward proxy, as these configurations are most susceptible to header manipulation attacks. Organizations relying on this software for web application security, content delivery, or load balancing are at risk of unauthorized access and data breaches if the vulnerability remains unpatched.
Security professionals should prioritize immediate remediation through official Apache Traffic Server updates that address the header validation issues. The vulnerability aligns with CWE-20, which specifically addresses "Improper Input Validation," and can be mapped to ATT&CK technique T1190 for "Proxy Through Command and Control" and T1566 for "Phishing with Social Engineering". Organizations should implement network monitoring to detect anomalous header patterns and consider deploying web application firewalls to mitigate potential exploitation attempts. Additionally, security teams should conduct thorough vulnerability assessments of their Apache Traffic Server deployments to ensure all affected versions have been updated and that proper input sanitization measures are in place to prevent similar issues in other components of their infrastructure stack.