CVE-2023-28755 is a vulnerability classified as a Regular Expression Denial of Service (ReDoS) affecting the URI parser component in Ruby versions through 3.2.1. The issue stems from the parser mishandling invalid URLs containing specific characters, which leads to excessive backtracking in the regular expression engine. This results in a significant increase in execution time when parsing such crafted URI strings, effectively causing a denial-of-service condition by exhausting CPU resources. The vulnerability does not compromise confidentiality or integrity but impacts availability by slowing or halting services that rely on URI parsing. Exploitation requires no authentication or user interaction, and the attack vector is remote, as an attacker can send maliciously crafted URIs to vulnerable applications. The vulnerability is tracked under CWE-1333, which relates to ReDoS issues caused by inefficient regular expressions. Fixed versions of Ruby addressing this vulnerability include 0.12.1, 0.11.1, 0.10.2, and 0.10.0.1. While no known exploits are currently reported in the wild, the medium CVSS score of 5.3 reflects the moderate impact and ease of exploitation. This vulnerability is particularly relevant for web applications and services written in Ruby that parse user-supplied URIs, where an attacker could disrupt service availability by triggering the ReDoS condition.

For European organizations, the primary impact of CVE-2023-28755 is on service availability. Applications and services that parse URIs using vulnerable Ruby versions may experience significant performance degradation or outages when processing maliciously crafted URLs. This can lead to denial-of-service conditions, affecting business continuity, customer experience, and potentially causing financial losses. Since the vulnerability does not affect confidentiality or integrity, data breaches are unlikely. However, availability disruptions can impact critical web services, APIs, and backend systems relying on Ruby for URI parsing. Organizations in sectors such as e-commerce, finance, government, and technology that deploy Ruby-based applications are at heightened risk. Additionally, the ease of remote exploitation without authentication increases the threat landscape, especially for publicly accessible services. The absence of known exploits in the wild suggests a window for proactive mitigation before widespread attacks occur.

To mitigate CVE-2023-28755, European organizations should prioritize upgrading Ruby to the fixed versions 0.12.1, 0.11.1, 0.10.2, or 0.10.0.1 as appropriate for their environment. Where immediate upgrades are not feasible, implement input validation to reject malformed or suspicious URI inputs before parsing. Employ rate limiting and request throttling on endpoints that accept URI inputs to reduce the risk of resource exhaustion from repeated malicious requests. Monitoring application performance and logs for unusual spikes in URI parsing times can help detect exploitation attempts early. Additionally, consider isolating URI parsing operations in separate processes or containers with resource limits to contain potential denial-of-service impacts. Regularly review and update dependency management practices to ensure timely application of security patches. Finally, conduct security awareness training for developers to recognize and mitigate ReDoS risks in code.