CVE-2019-16792 in Waitress
Summary
by MITRE
Waitress through version 1.3.1 allows request smuggling by sending the Content-Length header twice. Waitress would header fold a double Content-Length header and due to being unable to cast the now comma separated value to an integer would set the Content-Length to 0 internally. If two Content-Length headers are sent in a single request, Waitress would treat the request as having no body, thereby treating the body of the request as a new request in HTTP pipelining. This issue is fixed in Waitress 1.4.0.
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Analysis
by VulDB Data Team • 03/25/2024
CVE-2019-16792 represents a critical request smuggling vulnerability in the Waitress WSGI server that operates at the HTTP protocol level and can be exploited to manipulate request processing behavior. This vulnerability stems from Waitress's improper handling of HTTP headers, specifically when duplicate Content-Length headers are present in a single request. The flaw manifests when the server encounters multiple Content-Length headers, causing it to perform header folding operations that result in a comma-separated value. This comma-separated value cannot be properly converted to an integer, leading Waitress to internally set the Content-Length to zero, which effectively removes the request body from consideration. The vulnerability is categorized under CWE-1290, which deals with improper handling of HTTP headers, and aligns with ATT&CK technique T1190 for exploiting vulnerabilities in web applications.
The technical exploitation of this vulnerability relies on the HTTP pipelining mechanism and demonstrates a sophisticated understanding of how HTTP servers process request boundaries. When Waitress receives a request containing two Content-Length headers, it processes these headers through a folding mechanism that concatenates them into a comma-separated string. The server's inability to properly parse this comma-separated value as a single integer causes it to default to a Content-Length of zero, effectively treating the entire request body as if it were absent. This misinterpretation creates a scenario where the HTTP parser treats the body portion of the original request as a separate, independent HTTP request. The vulnerability is particularly dangerous because it allows an attacker to inject malicious requests into the pipeline, potentially leading to cross-site scripting, data manipulation, or unauthorized access to protected resources.
The operational impact of this vulnerability extends beyond simple request smuggling and can enable a range of malicious activities within the application server environment. Attackers can leverage this flaw to bypass authentication mechanisms, manipulate request routing, or perform unauthorized operations by injecting requests that appear to be part of the original transaction. The vulnerability affects the fundamental integrity of HTTP request processing, potentially allowing attackers to exploit other weaknesses in the application stack. Organizations using Waitress versions prior to 1.4.0 face significant risk as this vulnerability can be exploited without requiring authentication or specialized tools. The issue directly impacts web application security posture and can compromise the confidentiality, integrity, and availability of services running on affected servers. Security professionals should consider this vulnerability as part of broader HTTP protocol security assessments and implement proper header validation mechanisms.
Mitigation strategies for CVE-2019-16792 primarily involve upgrading to Waitress version 1.4.0 or later, which includes proper handling of duplicate Content-Length headers. Organizations should also implement robust input validation and sanitization measures at the application level, particularly for HTTP headers that are critical to request processing. Network-level protections such as web application firewalls can help detect and block malformed requests that attempt to exploit this vulnerability. Additionally, implementing proper monitoring and logging of HTTP request processing can help identify potential exploitation attempts. The fix implemented in Waitress 1.4.0 demonstrates a proper approach to handling edge cases in HTTP header processing by ensuring that duplicate headers are either properly merged or rejected rather than allowing the server to misinterpret the values. Security teams should conduct thorough testing of upgraded systems to ensure that the fix properly addresses the vulnerability without introducing regressions in application functionality. This vulnerability serves as a reminder of the importance of robust HTTP protocol implementation and the need for comprehensive security testing of web server components.