CVE-2023-51771 is a critical vulnerability identified in the MicroHttpServer (also known as Micro HTTP Server) component, specifically in the _ParseHeader function located in lib/server.c. The flaw is a one-byte buffer overflow occurring during the processing of an excessively long URI. This vulnerability is classified under CWE-120, which pertains to classic buffer overflow issues. The vulnerability arises because the _ParseHeader function does not properly validate or limit the length of the URI before copying it into a fixed-size buffer, allowing an attacker to overflow the buffer by sending a specially crafted HTTP request with an overly long URI. This overflow is a one-byte overflow, but even such minimal overflows can be exploited to overwrite adjacent memory, potentially leading to arbitrary code execution, denial of service, or other malicious outcomes. The CVSS v3.1 base score is 9.8, indicating a critical severity level. The vector string (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) indicates that the vulnerability is remotely exploitable over the network without any authentication or user interaction, and it impacts confidentiality, integrity, and availability to a high degree. No specific vendor or product version information is provided, which suggests that this vulnerability affects the MicroHttpServer project in general, possibly including multiple versions. There are no known exploits in the wild at the time of reporting, and no patches or mitigations have been linked yet. The vulnerability was published on December 25, 2023, and has been enriched by CISA, highlighting its importance for cybersecurity awareness and response.

For European organizations, the impact of CVE-2023-51771 could be severe, particularly for those using MicroHttpServer in embedded systems, IoT devices, or lightweight web server applications. Successful exploitation can lead to full system compromise, allowing attackers to execute arbitrary code remotely, disrupt services, or exfiltrate sensitive data. This can affect critical infrastructure sectors such as manufacturing, telecommunications, healthcare, and public administration, where embedded HTTP servers are often deployed. The lack of authentication and user interaction requirements means attackers can exploit this vulnerability at scale, potentially leading to widespread disruption. Additionally, the high impact on confidentiality, integrity, and availability could result in data breaches, operational downtime, and loss of trust. European organizations with limited patch management capabilities or those using legacy or custom implementations of MicroHttpServer are particularly at risk. The vulnerability also poses a threat to supply chain security if MicroHttpServer is embedded in third-party products used by European enterprises.

Given the absence of official patches, European organizations should take immediate and specific mitigation steps: 1) Conduct an inventory to identify all instances of MicroHttpServer usage within their environment, including embedded devices and custom applications. 2) Implement network-level protections such as Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) configured to detect and block HTTP requests with abnormally long URIs, effectively mitigating attempts to trigger the buffer overflow. 3) Apply strict input validation and URI length restrictions at the application or proxy level to prevent malicious requests from reaching vulnerable servers. 4) Isolate vulnerable devices or services from public networks where possible, restricting access to trusted internal networks only. 5) Monitor network traffic and logs for unusual patterns indicative of exploitation attempts, such as repeated long URI requests or crashes of MicroHttpServer instances. 6) Engage with vendors or open-source maintainers for updates or patches and plan for timely deployment once available. 7) Consider deploying host-based mitigations such as Address Space Layout Randomization (ASLR) and Data Execution Prevention (DEP) on affected systems to reduce exploitation success. 8) For embedded systems where patching is not feasible, evaluate replacement or firmware updates from device manufacturers. These targeted actions go beyond generic advice by focusing on the specific nature of the vulnerability and the operational context of MicroHttpServer deployments.