CVE-2023-28755 is a Regular Expression Denial of Service (ReDoS) vulnerability identified in the URI parsing component of Ruby programming language versions through 3.2.1. The vulnerability stems from the URI parser's mishandling of invalid URLs containing certain characters, which triggers excessive backtracking in the regular expression engine. This results in a significant increase in execution time when parsing these crafted URI strings, leading to potential denial of service conditions by exhausting CPU resources. The flaw does not compromise confidentiality or integrity but impacts availability by slowing or halting services that rely on URI parsing. Exploitation is straightforward as it requires no authentication or user interaction; an attacker can remotely send maliciously crafted URI strings to vulnerable applications. The issue is tracked under CWE-1333, which relates to ReDoS vulnerabilities caused by inefficient regular expressions. Fixed Ruby versions addressing this vulnerability include 0.12.1, 0.11.1, 0.10.2, and 0.10.0.1. No known exploits have been reported in the wild as of the publication date. The CVSS v3.1 base score is 5.3, reflecting medium severity with network attack vector, low attack complexity, no privileges required, no user interaction, and impact limited to availability. This vulnerability is particularly relevant for web applications and services developed in Ruby that parse user-supplied URIs, as they may be susceptible to denial of service attacks if not updated or mitigated.

For European organizations, this vulnerability poses a risk primarily to the availability of web applications and services that utilize Ruby for URI parsing. Denial of service attacks exploiting this flaw can lead to service outages, degraded performance, and potential disruption of business operations, especially for organizations relying on Ruby-based frameworks or custom applications that process external URI inputs. The impact is more pronounced in sectors with high web service dependency such as e-commerce, financial services, and public sector digital services. While the vulnerability does not expose sensitive data or allow unauthorized access, the resulting downtime can damage reputation, cause financial losses, and reduce customer trust. Additionally, organizations with stringent uptime requirements or those providing critical infrastructure services may face regulatory scrutiny if service disruptions occur. The absence of known exploits in the wild reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits over time.

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 soon as possible to eliminate the vulnerability. In environments where immediate upgrading is 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 data to reduce the risk of resource exhaustion. Monitoring application performance and logs for unusual spikes in URI parsing times can help detect attempted exploitation. Additionally, consider deploying Web Application Firewalls (WAFs) with rules designed to detect and block malicious URI patterns associated with ReDoS attacks. Conduct regular security assessments and code reviews focusing on regular expression usage and input handling in Ruby applications. Finally, maintain an incident response plan to quickly address potential denial of service incidents stemming from this vulnerability.