CVE-2025-12758 is a vulnerability identified in the validator package, specifically in versions prior to 13.15.22. The issue arises from the isLength() function's failure to correctly account for Unicode variation selectors (U+FE0F, U+FE0E) when calculating string length. Variation selectors are special Unicode characters that modify the appearance of preceding characters but do not contribute to the visible character count in a typical sense. The validator's incomplete filtering means that strings containing these selectors are miscounted as shorter than their actual byte length, allowing longer-than-expected input to bypass length checks. This improper validation can lead to multiple downstream issues: databases may truncate data unexpectedly, causing data integrity problems; buffer overflows may occur in components that assume validated input lengths, potentially leading to crashes or code execution; and denial-of-service attacks may be facilitated by resource exhaustion or application instability. The vulnerability is remotely exploitable without authentication or user interaction, increasing its risk profile. The CVSS 4.0 vector (AV:N/AC:L/AT:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:P) reflects a network attack vector with low complexity and no privileges or user interaction required, resulting in high impact on availability. No known exploits have been reported yet, but the potential impact warrants immediate attention. The vulnerability affects all applications using the vulnerable validator versions for input length validation, particularly those processing Unicode text inputs.

For European organizations, the impact of CVE-2025-12758 can be significant, especially for those relying on the validator package in web applications, APIs, or backend services that validate user input. Data truncation can lead to loss or corruption of critical information, affecting data integrity and business operations. Buffer overflows in downstream components may cause application crashes or open avenues for further exploitation, threatening system stability and security. Denial-of-service conditions could disrupt service availability, impacting customer trust and regulatory compliance, particularly under GDPR requirements for data accuracy and availability. Organizations in sectors such as finance, healthcare, and e-commerce, where data integrity and uptime are crucial, are at heightened risk. The vulnerability’s ease of exploitation without authentication means attackers can target exposed services directly, increasing the likelihood of attacks. Additionally, the widespread use of Node.js and validator in European software ecosystems amplifies the potential scope of affected systems.

To mitigate CVE-2025-12758, European organizations should immediately upgrade the validator package to version 13.15.22 or later, where the issue is resolved. Conduct a thorough audit of all applications and services that use validator for input length validation to identify and remediate any instances of the vulnerable function. Implement additional input validation layers that explicitly handle Unicode variation selectors to prevent bypass. Review database schemas and input handling logic to ensure they can safely accommodate inputs with variation selectors without truncation or overflow. Employ runtime application self-protection (RASP) or web application firewalls (WAF) with custom rules to detect anomalous input patterns that may exploit this vulnerability. Monitor application logs for unusual input lengths or error patterns indicative of exploitation attempts. Finally, integrate this vulnerability into vulnerability management and patching workflows to ensure timely updates in the future.