CVE-2017-7559 in Undertow
Summary
by MITRE
In Undertow 2.x before 2.0.0.Alpha2, 1.4.x before 1.4.17.Final, and 1.3.x before 1.3.31.Final, it was found that the fix for CVE-2017-2666 was incomplete and invalid characters are still allowed in the query string and path parameters. This could be exploited, in conjunction with a proxy that also permitted the invalid characters but with a different interpretation, to inject data into the HTTP response. By manipulating the HTTP response the attacker could poison a web-cache, perform an XSS attack, or obtain sensitive information from requests other than their own.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 01/20/2023
The vulnerability identified as CVE-2017-7559 represents a critical security flaw in the Undertow web server implementation that affects multiple version ranges including 2.x before 2.0.0.Alpha2, 1.4.x before 1.4.17.Final, and 1.3.x before 1.3.31.Final. This issue stems from an incomplete remediation of a previous vulnerability CVE-2017-2666, which demonstrates the complexity and potential for regressions in security patching processes. The flaw specifically targets the HTTP request parsing mechanisms within Undertow's handling of query strings and path parameters, where invalid characters that should have been properly sanitized are still being accepted and processed.
The technical nature of this vulnerability lies in the insufficient input validation mechanisms within Undertow's HTTP request parsing layer, which allows certain invalid characters to pass through the system's security controls. This incomplete fix creates a persistent security gap where malicious actors can exploit the system's tolerance for malformed HTTP requests. The vulnerability operates at the application layer of the OSI model and specifically impacts the HTTP protocol implementation within the Undertow framework, making it particularly dangerous as it can be leveraged to bypass security controls that rely on proper HTTP request sanitization.
From an operational impact perspective, this vulnerability enables attackers to perform sophisticated attacks including web cache poisoning, cross-site scripting exploitation, and unauthorized data access. The ability to manipulate HTTP responses through carefully crafted invalid characters allows adversaries to inject malicious content into web caches, potentially affecting multiple users who access cached content. Additionally, the vulnerability can be exploited to execute XSS attacks against unsuspecting users, as well as to obtain sensitive information from other users' requests through response manipulation techniques. This makes the vulnerability particularly dangerous in environments where Undertow serves as a reverse proxy or load balancer component.
The exploitation of CVE-2017-7559 aligns with several ATT&CK tactics including T1190 (Exploit Public-Facing Application) and T1071.004 (Application Layer Protocol: DNS) when combined with proxy configurations that may interpret the same invalid characters differently. The vulnerability also corresponds to CWE-20 (Improper Input Validation) and CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer) as it involves both inadequate validation of input parameters and potential memory handling issues during HTTP request processing. Organizations using Undertow in production environments should prioritize immediate patching to address this vulnerability, as the incomplete fix creates a persistent attack surface that can be leveraged by threat actors to compromise web applications and user data.
Security practitioners should implement network-level monitoring to detect unusual HTTP request patterns that might indicate exploitation attempts, particularly focusing on malformed query strings and path parameters. The vulnerability demonstrates the importance of thorough regression testing when applying security patches and highlights the need for comprehensive input validation across all HTTP request components. Organizations should also consider implementing web application firewalls and additional security controls to mitigate potential exploitation attempts while awaiting official patches. The incident serves as a reminder of the critical nature of proper HTTP request parsing and validation in web server implementations, where incomplete security fixes can create dangerous persistent vulnerabilities in widely used software components.