CVE-2017-6508 in wget
Summary
by MITRE
CRLF injection vulnerability in the url_parse function in url.c in Wget through 1.19.1 allows remote attackers to inject arbitrary HTTP headers via CRLF sequences in the host subcomponent of a URL.
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Analysis
by VulDB Data Team • 03/07/2017
The CVE-2017-6508 vulnerability represents a critical cross-site scripting and header injection flaw within the Wget web client software. This vulnerability specifically affects versions 1.19.1 and earlier, where the url_parse function in the url.c source file fails to properly sanitize input containing carriage return line feed sequences. The flaw enables remote attackers to inject malicious HTTP headers into requests, potentially allowing for various malicious activities including cache poisoning, session hijacking, and transparent proxy attacks. The vulnerability occurs when Wget processes URLs that contain CRLF sequences within the host component, which should normally be rejected or properly encoded.
The technical exploitation of this vulnerability stems from insufficient input validation within Wget's URL parsing mechanism. When a malicious URL containing CRLF characters is processed, the url_parse function does not adequately filter or escape these sequences before constructing HTTP requests. This creates an injection vector where attackers can insert arbitrary HTTP headers into the request, effectively bypassing normal security controls. The vulnerability is classified under CWE-117, which specifically addresses improper output neutralization for logs, and aligns with ATT&CK technique T1071.004 for application layer protocol tunneling. The flaw essentially allows attackers to manipulate the HTTP request headers, potentially enabling them to inject malicious content that gets processed by the target server or intermediate proxies.
The operational impact of CVE-2017-6508 extends beyond simple header injection, as it can lead to significant security breaches in environments where Wget is used for automated downloads or web scraping. Attackers could exploit this vulnerability to perform cache poisoning attacks against web servers, manipulate HTTP responses, or even redirect traffic through transparent proxies. The vulnerability particularly affects systems that rely on Wget for automated tasks, including build systems, security scanners, and automated backup solutions that may process untrusted URLs from external sources. This creates a vector for attackers to compromise not only the immediate target but potentially entire networks if Wget is used in enterprise environments where it processes URLs from multiple sources.
Mitigation strategies for CVE-2017-6508 primarily involve upgrading to Wget version 1.19.2 or later, which contains the necessary patches to properly sanitize CRLF sequences in URL parsing. Organizations should also implement strict input validation for any URLs processed by Wget, particularly in automated environments where external input is accepted. Network administrators should monitor for suspicious HTTP header patterns and implement proper logging to detect potential exploitation attempts. Additional protective measures include configuring Wget to use strict URL validation, implementing proxy filtering rules, and ensuring that automated systems do not process URLs from untrusted sources without proper sanitization. The vulnerability demonstrates the importance of proper input validation and output encoding in client-side applications, particularly when handling network protocols where header injection attacks can have far-reaching consequences across the entire web infrastructure.