Overview
CVE-2025-12758 is a high-severity vulnerability affecting versions of the popular JavaScript package validator before 13.15.22. This vulnerability stems from an incomplete filtering of Unicode variation selectors within the isLength() function, leading to inaccurate string length calculations. This can allow attackers to bypass length-based input validation, potentially causing significant security issues in applications using the affected versions of the library.
Technical Details
The isLength() function in vulnerable versions of validator.js fails to correctly account for Unicode variation selectors (specifically \uFE0F and \uFE0E). These selectors are used to specify the desired visual representation of a character. The vulnerability arises because the function doesn’t exclude these selectors when calculating the length of a string. This allows an attacker to craft input strings that appear shorter than their actual length to the isLength() function, while actually exceeding the expected limits when processed by other parts of the application.
For example, an input field limited to 20 characters could accept a string containing numerous Unicode variation selectors, resulting in a significantly longer string being processed by the backend, potentially leading to buffer overflows, data truncation, or other vulnerabilities.
CVSS Analysis
- CVE ID: CVE-2025-12758
- Severity: HIGH
- CVSS Score: 7.5
A CVSS score of 7.5 indicates a high-severity vulnerability. This score reflects the potential for attackers to exploit this flaw without requiring significant privileges, leading to a considerable impact on confidentiality, integrity, and availability.
Possible Impact
The exploitation of CVE-2025-12758 can have serious consequences, including:
- Data Truncation: If
isLength()is used to validate input before storing it in a database, an attacker could bypass the validation and insert data that exceeds the column size, leading to data truncation and potential data loss. - Buffer Overflows: If the validated string is subsequently used in operations that are susceptible to buffer overflows, an attacker could exploit this vulnerability to execute arbitrary code.
- Denial-of-Service (DoS): Crafted strings containing a large number of Unicode variation selectors can consume excessive resources when processed, potentially leading to a denial-of-service condition.
- Bypassing Security Measures: Any security measure that relies on the
isLength()function of the vulnerable library to enforce length limitations on user input can be bypassed.
Mitigation and Patch Steps
The most effective way to mitigate CVE-2025-12758 is to upgrade to validator.js version 13.15.22 or later. This version contains a fix that properly handles Unicode variation selectors. Follow these steps:
- Update
validator.js: Use your package manager (e.g., npm, yarn) to update thevalidatorpackage to the latest version. For example, using npm:npm install validator@latest - Verify the Update: After updating, verify that the installed version is 13.15.22 or later.
- Review Code: Review your application’s code to ensure that
isLength()is not being relied upon without proper sanitization or encoding of user input. Consider adding additional validation layers. - Testing: Thoroughly test your application after the update to ensure that the vulnerability has been successfully mitigated and that no new issues have been introduced.
