CVE-2023-30421 is a vulnerability classified under CWE-407 (Inefficient Algorithmic Complexity) found in the mjson project, specifically affecting version 1.2.7. The issue resides in the 'mystrtod' function, which is responsible for parsing string representations of floating-point numbers. When processing certain crafted digit strings, such as '8891110122900e913013935755114', the function requires more than a billion iterations to complete. This excessive computational effort leads to a significant degradation in performance, effectively causing a denial-of-service (DoS) condition by consuming excessive CPU resources. The vulnerability does not appear to require authentication or user interaction to be triggered, as it is related to input processing. No known exploits are currently reported in the wild, and no official patches have been published yet. The root cause is an inefficient algorithmic approach to parsing specific numeric strings, which can be exploited by an attacker to overwhelm systems using the vulnerable mjson library. Given that mjson is a lightweight JSON parser used in various applications and embedded systems, any software relying on version 1.2.7 could be susceptible to this resource exhaustion attack if they process untrusted input containing maliciously crafted numeric strings.

For European organizations, the primary impact of this vulnerability is the potential for denial-of-service attacks against services and applications that utilize the vulnerable mjson 1.2.7 library. This could lead to service outages, degraded performance, and increased operational costs due to resource exhaustion. Critical infrastructure, financial services, and industrial control systems that embed mjson for JSON parsing could be disrupted, affecting availability and potentially causing cascading failures. Since the vulnerability exploits inefficient parsing of numeric strings, any externally facing API or service that accepts JSON input without proper input validation is at risk. The impact on confidentiality and integrity is minimal, as the vulnerability does not allow for data leakage or unauthorized modification. However, the availability impact can be significant, especially for high-availability systems. European organizations with automated data processing pipelines, IoT deployments, or embedded systems using mjson are particularly vulnerable. The lack of known exploits in the wild suggests a window of opportunity for proactive mitigation before widespread exploitation occurs.

1. Immediate mitigation involves upgrading or patching the mjson library to a version that addresses this inefficient algorithmic complexity issue once available. Since no official patch is currently published, organizations should monitor vendor advisories closely. 2. Implement input validation and sanitization to detect and reject unusually large or malformed numeric strings before they reach the mjson parser. 3. Employ application-layer rate limiting and anomaly detection to identify and block suspicious JSON payloads that could trigger excessive parsing iterations. 4. Use resource limiting techniques such as CPU usage quotas or sandboxing for processes handling untrusted JSON input to contain potential DoS impacts. 5. Where feasible, replace mjson with alternative JSON parsing libraries known to be resilient against algorithmic complexity attacks. 6. Conduct code audits and penetration testing focusing on JSON input handling to identify similar inefficiencies. 7. Monitor system performance metrics and logs for signs of abnormal CPU spikes correlated with JSON processing activities. These targeted mitigations go beyond generic advice by focusing on input validation, resource containment, and proactive monitoring specific to the nature of this vulnerability.