CVE-2024-27280 is a buffer-overread vulnerability identified in the StringIO library versions 3.0.1 bundled with Ruby versions 3.0.x through 3.0.6 and 3.1.x through 3.1.4. The vulnerability arises from improper bounds checking in the ungetbyte and ungetc methods, which allow reading past the end of the internal string buffer. When these methods are used, a subsequent call to StringIO.gets can return memory contents beyond the intended string boundary, potentially exposing sensitive data residing in adjacent memory. This type of vulnerability is classified under CWE-120 (Classic Buffer Overflow). The CVSS 3.1 base score is 9.8 (critical), reflecting that the vulnerability can be exploited remotely (AV:N), with low attack complexity (AC:L), no privileges required (PR:N), and no user interaction needed (UI:N). The impact affects confidentiality, integrity, and availability (C:H/I:H/A:H), indicating that an attacker could leak sensitive information, corrupt data, or cause denial of service. Fixed versions have been released: StringIO 3.0.1.1 for Ruby 3.0 and 3.0.1.2 for Ruby 3.1, with 3.0.3 as the main fixed version. No public exploits or active exploitation have been reported yet, but the severity and ease of exploitation make this a critical issue for any Ruby-based environment using affected versions.

For European organizations, the impact of CVE-2024-27280 can be significant, especially for those relying on Ruby for web applications, backend services, or automation scripts. The vulnerability allows attackers to read memory beyond intended boundaries, potentially exposing sensitive information such as credentials, cryptographic keys, or personal data, which could lead to data breaches and regulatory non-compliance under GDPR. The integrity of applications may also be compromised if attackers manipulate memory contents, leading to corrupted data or application crashes, impacting availability. Given Ruby's widespread use in startups, financial services, and government digital services across Europe, exploitation could disrupt critical services and damage organizational reputation. The lack of required privileges or user interaction lowers the barrier for attackers, increasing the risk of automated exploitation attempts. Organizations with public-facing Ruby applications or internal systems using vulnerable versions are particularly at risk.

European organizations should immediately identify all Ruby environments running versions 3.0.x through 3.0.6 and 3.1.x through 3.1.4, especially those using the StringIO library. They must upgrade to the fixed versions: StringIO 3.0.1.1 for Ruby 3.0 and 3.0.1.2 for Ruby 3.1, or Ruby 3.0.3 as the main fixed version. Where immediate patching is not feasible, organizations should audit code to detect usage of ungetbyte and ungetc methods on StringIO objects and implement temporary mitigations such as input validation or restricting access to vulnerable components. Employ runtime application self-protection (RASP) or memory protection tools to detect anomalous memory reads. Conduct thorough security testing and code reviews focusing on buffer handling. Additionally, monitor network traffic and logs for unusual activity indicative of exploitation attempts. Implement strict access controls and network segmentation to limit exposure of vulnerable systems. Finally, update incident response plans to include this vulnerability and prepare for potential exploitation scenarios.