CVE-2021-3466 in libmicrohttpd
Summary
by MITRE • 03/25/2021
A flaw was found in libmicrohttpd in versions before 0.9.71. A missing bounds check in the post_process_urlencoded function leads to a buffer overflow, allowing a remote attacker to write arbitrary data in an application that uses libmicrohttpd. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.
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Analysis
by VulDB Data Team • 04/05/2021
The vulnerability identified as CVE-2021-3466 represents a critical buffer overflow flaw within the libmicrohttpd library, a widely-used embedded HTTP server library that serves as the foundation for numerous applications requiring lightweight web server capabilities. This vulnerability specifically affects versions prior to 0.9.71 and stems from a fundamental missing bounds check in the post_process_urlencoded function, which processes URL-encoded data submitted through HTTP POST requests. The flaw occurs when the library fails to properly validate the length of incoming data against the allocated buffer space, creating a condition where attacker-controlled input can exceed the designated memory boundaries and overwrite adjacent memory regions. The technical nature of this vulnerability places it squarely within the CWE-121 category of stack-based buffer overflow, though it manifests in a heap-based context due to the dynamic memory allocation patterns employed by the library.
The operational impact of this vulnerability extends beyond simple data corruption, presenting a comprehensive threat vector that compromises multiple aspects of system security and stability. Remote attackers can exploit this flaw to execute arbitrary code within the context of the affected application, potentially leading to complete system compromise or unauthorized access to sensitive data. The vulnerability's ability to affect data confidentiality means that attackers can intercept or modify sensitive information transmitted through HTTP connections, while the integrity implications suggest that system data could be altered or corrupted. Additionally, the availability threat manifests through potential denial-of-service conditions where carefully crafted payloads can cause application crashes or system instability, rendering services unavailable to legitimate users. The exploitability of this vulnerability is particularly concerning given that libmicrohttpd is integrated into numerous applications, including network services, embedded systems, and IoT devices, amplifying the potential attack surface significantly.
Security practitioners should consider this vulnerability in the context of the MITRE ATT&CK framework, particularly under the T1059.007 technique for command and script interpreter, as successful exploitation could enable attackers to execute malicious code and establish persistent access. The vulnerability also maps to T1566.001 for spearphishing attachments and T1210 for exploitation of remote services, as it represents a classic remote code execution vector that can be leveraged through web-based attack surfaces. Organizations utilizing libmicrohttpd should prioritize immediate patching to version 0.9.71 or later, as this represents the first release containing the necessary bounds checking mechanisms to prevent the buffer overflow condition. Additional mitigations include implementing network segmentation to limit exposure of affected applications, deploying web application firewalls to filter suspicious HTTP requests, and conducting thorough code reviews of applications that rely on libmicrohttpd to identify potential secondary vulnerabilities or improper input handling patterns that could compound the risk. System administrators should also monitor for unusual network traffic patterns or application behavior that might indicate exploitation attempts, as the vulnerability's remote nature makes it particularly suitable for automated exploitation campaigns targeting vulnerable systems across the internet.