CVE-2019-11236 in urllib3
Summary
by MITRE
In the urllib3 library through 1.24.1 for Python, CRLF injection is possible if the attacker controls the request parameter.
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Analysis
by VulDB Data Team • 10/13/2024
The vulnerability identified as CVE-2019-11236 represents a critical CRLF (Carriage Return Line Feed) injection flaw within the urllib3 library version 1.24.1 and earlier. This library serves as a fundamental HTTP library for Python applications, making it a widespread component across numerous software systems. The vulnerability arises from insufficient input validation and sanitization of user-controlled parameters within HTTP request construction, creating an avenue for attackers to inject malicious CRLF sequences that can manipulate HTTP headers and request behavior. The flaw specifically manifests when applications using urllib3 construct HTTP requests where user input directly influences request parameters, allowing malicious actors to inject line terminators that can alter the HTTP protocol flow.
The technical exploitation of this vulnerability occurs through the manipulation of HTTP request parameters that are processed by urllib3 without proper sanitization of CRLF characters. When an attacker controls input that flows into HTTP request construction, they can inject sequences such as %0d%0a or \r\n directly into headers or URL components. This injection capability enables multiple attack vectors including HTTP response splitting, cache poisoning, and header manipulation that can lead to session hijacking, cross-site scripting, or man-in-the-middle attacks. The vulnerability operates at the protocol level where HTTP headers are constructed, making it particularly dangerous as it can bypass traditional security controls that operate at higher application layers.
The operational impact of CVE-2019-11236 extends beyond individual applications to affect entire ecosystems that rely on urllib3 for HTTP communication. Given that urllib3 is a dependency for popular Python libraries such as requests, the vulnerability can compromise a vast array of web applications, APIs, and microservices. Attackers can leverage this flaw to manipulate HTTP responses, inject malicious content into web caches, or redirect traffic through header manipulation, potentially leading to significant data breaches or service disruption. The vulnerability's severity is compounded by its prevalence, as many Python-based web applications and frameworks depend on urllib3 for their HTTP communication capabilities, making it a prime target for exploitation.
Mitigation strategies for CVE-2019-11236 require immediate remediation through library updates to version 1.24.2 or later, where the CRLF injection vulnerability has been addressed through proper input sanitization and validation. Organizations should implement comprehensive dependency management practices to ensure all Python applications are updated to patched versions of urllib3 and related libraries. Additionally, input validation should be implemented at multiple layers including application-level sanitization of user-controlled parameters, network-level filtering of HTTP headers, and regular security scanning of dependencies. The vulnerability aligns with CWE-113, which describes improper neutralization of CRLF sequences in HTTP headers, and can be mapped to ATT&CK technique T1071.004 for application layer protocol manipulation. Security teams should also consider implementing web application firewalls and HTTP header validation rules as additional defensive measures to detect and prevent exploitation attempts.