CVE-2018-20356 in Mongoose Embedded Web Server Library
Summary
by MITRE
An invalid read of 8 bytes due to a use-after-free vulnerability in the mg_http_free_proto_data_cgi function call in mongoose.c in Cesanta Mongoose Embedded Web Server Library 6.13 and earlier allows a denial of service (application crash) or remote code execution.
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Analysis
by VulDB Data Team • 10/03/2023
The vulnerability identified as CVE-2018-20356 represents a critical use-after-free condition within the Cesanta Mongoose Embedded Web Server Library version 6.13 and earlier. This flaw manifests in the mg_http_free_proto_data_cgi function where an invalid read of 8 bytes occurs, creating a scenario where freed memory is accessed beyond its intended lifecycle. The vulnerability stems from improper memory management practices where the web server library fails to properly invalidate pointers or clear memory references after objects have been deallocated, allowing subsequent access to already freed memory locations.
The technical exploitation of this vulnerability follows a predictable pattern where an attacker can craft malicious HTTP requests that trigger the specific code path leading to the use-after-free condition. When the mg_http_free_proto_data_cgi function processes certain protocol data structures, it attempts to access memory that has already been freed by previous operations, resulting in either an application crash or more critically, potential remote code execution. This memory corruption occurs during the cleanup phase of HTTP protocol handling, specifically when processing CGI (Common Gateway Interface) data, making it particularly dangerous in web server environments where CGI processing is common. The vulnerability falls under CWE-416 which specifically addresses use-after-free conditions, and aligns with ATT&CK technique T1203 for legitimate program execution and T1059 for command and scripting interpreter usage.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to encompass potential remote code execution capabilities that could allow attackers to compromise entire web server installations. When exploited successfully, the vulnerability could enable attackers to execute arbitrary code on the target system with the privileges of the web server process, potentially leading to full system compromise. The embedded nature of the Mongoose library means that this vulnerability affects a wide range of applications that utilize this web server component, including IoT devices, embedded systems, and custom applications that rely on the library for HTTP functionality. The memory corruption pattern suggests that attackers could potentially leverage this vulnerability to manipulate the program execution flow through controlled data manipulation, making it particularly attractive for advanced persistent threat actors.
Mitigation strategies for CVE-2018-20356 must focus on immediate remediation through library version updates to 6.14 or later where the memory management issues have been addressed. Organizations should conduct thorough inventory assessments to identify all systems utilizing affected versions of the Cesanta Mongoose library and prioritize patching efforts accordingly. Additionally, network segmentation and access controls should be implemented to limit exposure of vulnerable web server instances to untrusted networks. Input validation measures should be strengthened to prevent malicious HTTP requests from reaching the vulnerable code paths, while also implementing memory safety checks and address space layout randomization to complicate exploitation attempts. Regular security auditing of embedded systems and third-party libraries remains crucial for early detection of similar vulnerabilities, as this flaw demonstrates the importance of proper memory management in embedded web server implementations. The vulnerability highlights the necessity of adhering to secure coding practices and memory safety standards as outlined in industry best practices for embedded systems development and web server security hardening.