CVE-2019-20800 in Cherokee
Summary
by MITRE
In Cherokee through 1.2.104, remote attackers can trigger an out-of-bounds write in cherokee_handler_cgi_add_env_pair in handler_cgi.c by sending many request headers, as demonstrated by a GET request with many "Host: 127.0.0.1" headers.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 05/18/2020
The vulnerability CVE-2019-20800 represents a critical out-of-bounds write flaw in the Cherokee web server version 1.2.104 and earlier. This security issue resides within the CGI handler component of the web server software, specifically in the cherokee_handler_cgi_add_env_pair function located in the handler_cgi.c source file. The flaw manifests when the server processes HTTP requests containing an excessive number of headers, creating a condition where memory boundaries are exceeded during the processing of environment variables for CGI scripts.
The technical exploitation of this vulnerability occurs through a carefully crafted HTTP GET request that includes an excessive number of identical Host headers, such as multiple "Host: 127.0.0.1" entries. When the Cherokee web server processes these malformed requests, the handler_cgi_add_env_pair function fails to properly validate the number of headers being processed, leading to a buffer overflow condition. This type of vulnerability falls under the CWE-121 CWE category for stack-based buffer overflow, where the program writes beyond the allocated memory boundaries for the environment variable array.
The operational impact of this vulnerability extends beyond simple denial of service, as it creates potential for remote code execution and system compromise. Attackers can leverage this flaw to overwrite adjacent memory locations, potentially corrupting program execution flow or injecting malicious code into the web server process. The vulnerability affects the core functionality of the Cherokee web server's CGI processing capabilities, which are commonly used for executing server-side scripts and handling dynamic content generation. This makes the impact particularly severe for web applications that rely on CGI functionality for user authentication, data processing, or other critical operations.
From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1203 - Exploitation for Client Execution, where attackers exploit memory corruption vulnerabilities to gain unauthorized access to systems. The attack surface is significant as CGI handlers are frequently used in web applications, and the vulnerability can be exploited through standard HTTP traffic without requiring authentication or specialized tools. Organizations using Cherokee web server versions prior to 1.2.105 should immediately implement mitigations including upgrading to patched versions, implementing request header rate limiting, and deploying web application firewalls to detect and block malformed requests containing excessive headers. The vulnerability also highlights the importance of input validation and bounds checking in server-side applications, particularly when processing user-provided data such as HTTP headers that can be easily manipulated by remote attackers.
This vulnerability demonstrates the critical importance of proper memory management and input validation in web server software, as the flaw exists in a fundamental component responsible for handling HTTP request processing. The out-of-bounds write condition creates a potential pathway for attackers to escalate privileges or execute arbitrary code on the affected system, making it a high-priority security concern for organizations relying on Cherokee web server deployments. The vulnerability's exploitation requires minimal effort from attackers, making it particularly dangerous in production environments where web servers are constantly exposed to internet traffic and potential malicious input.