CVE-2025-27209 is a vulnerability identified in Node.js version 24.0.0 stemming from a change in the V8 JavaScript engine's string hashing mechanism. The V8 engine switched to using rapidhash for computing string hashes, which inadvertently reintroduced a HashDoS vulnerability (CWE-407). HashDoS attacks exploit the hash function's susceptibility to collisions, where an attacker crafts numerous input strings that hash to the same value. This causes hash table operations, such as lookups or insertions, to degrade from average O(1) time complexity to O(n), leading to significant CPU resource exhaustion. Notably, the attacker does not need knowledge of the hash seed, simplifying exploitation. The vulnerability affects Node.js 24.x users, specifically version 24.0.0, and can be triggered remotely without authentication or user interaction, as it relies on attacker-controlled input strings processed by the Node.js runtime. The CVSS v3.0 score of 7.5 reflects a high severity due to the network attack vector, low attack complexity, and the potential for complete denial of service (availability impact). No patches or exploits are currently documented, but the risk is substantial given Node.js's widespread use in web applications and services. The vulnerability's root cause is a regression in the V8 engine's hashing algorithm, emphasizing the importance of thorough testing when modifying fundamental components like hash functions.

For European organizations, the primary impact of CVE-2025-27209 is the risk of denial of service attacks against Node.js applications running version 24.0.0. This can lead to service outages, degraded performance, and potential loss of availability for critical web services, APIs, or backend systems. Industries relying heavily on Node.js for real-time applications, e-commerce platforms, or cloud services could experience operational disruptions. The vulnerability does not compromise confidentiality or integrity directly but can indirectly affect business continuity and user trust. Given the ease of exploitation without authentication, attackers can launch large-scale or targeted DoS campaigns remotely. Organizations in sectors such as finance, telecommunications, and government services, which often deploy Node.js-based solutions, may face increased risk. Additionally, the lack of known exploits in the wild suggests a window for proactive mitigation before widespread attacks occur.

1. Upgrade Node.js: Monitor official Node.js releases and promptly upgrade to a patched version that addresses the HashDoS vulnerability once available. 2. Input Validation: Implement strict input validation and sanitization on all user-controlled strings that are processed or hashed to reduce the likelihood of crafted collision inputs. 3. Rate Limiting: Deploy rate limiting and throttling mechanisms on APIs and services to limit the number of requests from a single source, mitigating the impact of collision-based DoS attempts. 4. Monitoring and Alerting: Enhance monitoring for unusual CPU usage patterns and request anomalies that may indicate hash collision attacks. 5. Use Alternative Hashing: Where feasible, configure or patch applications to use more collision-resistant hashing algorithms or libraries. 6. Isolate Critical Services: Architect services to isolate Node.js components handling untrusted input, minimizing the blast radius of potential attacks. 7. Engage with Vendors: Coordinate with third-party vendors and cloud providers to ensure they are aware of the vulnerability and have applied necessary patches or mitigations.