CVE-2017-2666 in Undertow
Summary
by MITRE
It was discovered in Undertow that the code that parsed the HTTP request line permitted invalid characters. 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.
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Analysis
by VulDB Data Team • 04/27/2023
The vulnerability identified as CVE-2017-2666 resides within the Undertow web server implementation, specifically in its HTTP request line parsing mechanism. This flaw represents a classic input validation issue that undermines the fundamental security assumptions of HTTP protocol handling. The vulnerability stems from the server's permissive approach to character validation during HTTP request line processing, allowing malformed sequences that should normally be rejected by compliant HTTP parsers.
The technical exploitation of this vulnerability leverages a specific parsing inconsistency between Undertow and proxy servers that may handle the same invalid characters differently. When an attacker crafts HTTP requests containing these permitted but invalid characters, the Undertow server processes them according to its lenient parsing rules while a downstream proxy interprets the same characters differently. This discrepancy creates a condition where data injection becomes possible within HTTP responses generated by the vulnerable server. The flaw operates at the protocol level, specifically targeting the HTTP request line parsing component that should strictly validate the format and character set of incoming requests.
The operational impact of this vulnerability extends beyond simple data corruption, enabling sophisticated attack vectors that can compromise web application security. Attackers can leverage this weakness to poison web caches, effectively serving malicious content to other users who might access cached responses. The vulnerability also facilitates cross-site scripting attacks by allowing injection of malicious scripts into HTTP responses that are subsequently rendered by user browsers. Additionally, the flaw enables information disclosure attacks where an attacker might extract sensitive data from other users' requests, creating a serious privacy and confidentiality risk within web applications that rely on Undertow as their HTTP server implementation.
This vulnerability aligns with CWE-20, which describes improper input validation, and represents a specific instance of protocol-level parsing inconsistencies that can lead to injection attacks. From an ATT&CK framework perspective, this weakness maps to techniques involving protocol manipulation and response injection, potentially enabling cache poisoning and XSS execution. The vulnerability also intersects with ATT&CK's data exposure categories, as it can facilitate unauthorized data access through response manipulation. Organizations implementing Undertow-based web applications should consider this vulnerability as part of broader security assessments, particularly when proxy configurations are involved. The remediation strategy requires implementing stricter HTTP request line validation and ensuring consistent character interpretation across all components in the HTTP request processing pipeline. Security teams should also implement monitoring for unusual HTTP request patterns that might indicate exploitation attempts, while maintaining proper input sanitization and output encoding practices to prevent cascading effects of such vulnerabilities in complex web application architectures.