CVE-2025-6494 is a heap-based buffer overflow vulnerability identified in the Nokogiri library, specifically affecting versions 1.18.0 through 1.18.7. Nokogiri is a widely used Ruby gem for parsing HTML, XML, and other markup languages, leveraging the Gumbo parser internally. The vulnerability resides in the function hashmap_get_with_hash within the file gumbo-parser/src/hashmap.c. This function is responsible for retrieving elements from a hashmap data structure, and improper handling of input data leads to a heap-based buffer overflow condition. Such a flaw can cause memory corruption, potentially allowing an attacker to execute arbitrary code or cause a denial of service by crashing the application. The vulnerability requires local access with low privileges (PR:L) and does not require user interaction (UI:N). The attack complexity is low (AC:L), and no authentication is needed (AT:N). The CVSS v4.0 base score is 4.8, categorizing it as a medium severity issue. Although the exploit has been publicly disclosed, there are no known exploits in the wild at the time of publication. The vulnerability affects only local attackers who can execute code on the target system, which limits the attack surface. However, given Nokogiri's widespread use in web applications, development tools, and automation scripts, the risk remains significant in environments where untrusted local code execution is possible. The vulnerability does not impact confidentiality, integrity, or availability directly over a network, but local exploitation could lead to privilege escalation or application crashes. No official patches or updates have been linked yet, so mitigation relies on restricting local access and monitoring for suspicious activity.

For European organizations, the impact of CVE-2025-6494 is primarily relevant in environments where Nokogiri is used in local processing contexts, such as development workstations, CI/CD pipelines, or internal automation tools. Since the vulnerability requires local access, the risk is higher in organizations with large developer teams, shared workstations, or environments where untrusted users have local system access. Exploitation could lead to application crashes or arbitrary code execution, potentially allowing attackers to escalate privileges or move laterally within internal networks. This could disrupt business operations, compromise sensitive data processed locally, or undermine the integrity of software development processes. Sectors with high reliance on Ruby-based applications, such as financial services, technology firms, and research institutions, may face elevated risks. The medium severity rating suggests that while the vulnerability is not critical, it should not be ignored, especially in environments with lax local access controls. The lack of known exploits in the wild reduces immediate threat levels but does not preclude future attacks. European organizations must consider the potential for insider threats or compromised local accounts to leverage this vulnerability.

Immediately restrict local access to systems running vulnerable Nokogiri versions to trusted personnel only. Implement strict user privilege management and enforce the principle of least privilege to minimize the risk of local exploitation. Monitor local system logs and application behavior for anomalies indicative of exploitation attempts, such as unexpected crashes or memory errors in Nokogiri-dependent applications. Where possible, isolate development and build environments to prevent untrusted code execution on systems with Nokogiri installed. Apply virtual patching or runtime application self-protection (RASP) techniques to detect and block suspicious calls to the vulnerable hashmap_get_with_hash function until an official patch is released. Engage with the Nokogiri maintainers or community to obtain updates or patches as soon as they become available and plan prompt deployment. Conduct internal audits to identify all instances of Nokogiri usage across the organization, including embedded or indirect dependencies, to ensure comprehensive coverage. Educate developers and system administrators about the vulnerability and the importance of local system security hygiene.