CVE-2017-5660 in Traffic Server
Summary
by MITRE
There is a vulnerability in Apache Traffic Server (ATS) 6.2.0 and prior and 7.0.0 and prior with the Host header and line folding. This can have issues when interacting with upstream proxies and the wrong host being used.
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Analysis
by VulDB Data Team • 01/09/2020
The vulnerability identified as CVE-2017-5660 affects Apache Traffic Server versions 6.2.0 and earlier, as well as 7.0.0 and earlier, presenting a significant security risk related to Host header processing and line folding mechanisms. This flaw specifically manifests when ATS interacts with upstream proxy servers, creating potential for incorrect host resolution and routing decisions that could be exploited by malicious actors. The vulnerability stems from improper handling of HTTP Host headers that contain line folding sequences, which can cause the server to misinterpret the intended destination host.
The technical implementation of this vulnerability involves the way Apache Traffic Server processes HTTP headers, particularly when encountering line folding in Host header values. Line folding occurs when HTTP header values are split across multiple lines using specific line continuation mechanisms, typically involving spaces or tabs at the beginning of continuation lines. When ATS encounters such malformed headers, it may incorrectly parse the Host header, potentially extracting a different host value than intended or failing to properly validate the header content. This parsing error can lead to requests being forwarded to unintended upstream servers or proxies, creating potential for man-in-the-middle attacks or unauthorized access to backend systems.
The operational impact of CVE-2017-5660 extends beyond simple request routing errors, as it can enable attackers to manipulate the host resolution process within the proxy chain. When ATS processes requests with malformed Host headers, it may forward traffic to different servers than those specified in the original request, potentially exposing internal network resources or redirecting traffic to malicious endpoints. This vulnerability particularly affects environments where ATS serves as a reverse proxy or forward proxy, where proper host validation is critical for maintaining network security boundaries. The risk is amplified in complex proxy hierarchies where multiple intermediate proxies may be involved in the request processing chain.
The vulnerability aligns with CWE-1035, which addresses issues related to improper handling of HTTP headers and line folding in web applications and proxy servers. This classification indicates that the flaw represents a common pattern in HTTP processing implementations where header validation and parsing logic fails to properly account for various header formatting conventions. From an ATT&CK framework perspective, this vulnerability maps to techniques involving proxy manipulation and network traffic interception, potentially enabling adversaries to perform request smuggling or cache poisoning attacks. Organizations utilizing Apache Traffic Server in production environments should consider this vulnerability as part of their broader security posture assessment, particularly in scenarios involving multi-tier proxy architectures.
Mitigation strategies for CVE-2017-5660 primarily involve upgrading to Apache Traffic Server versions 6.2.1 or 7.0.1 and later, which contain fixes for the Host header parsing logic. Administrators should also implement additional header validation measures at the network level, including the enforcement of strict HTTP header parsing rules and the implementation of proper input sanitization for all incoming requests. Network monitoring should be enhanced to detect anomalous Host header patterns that might indicate exploitation attempts, while access controls should be reviewed to ensure that only authorized hosts can be specified in proxy requests. The fix implemented in newer versions addresses the core parsing logic to properly handle line folding sequences in Host headers, ensuring that the intended destination host is correctly identified and processed during request forwarding operations.