CVE-2026-6991: Zod CUID Handler SQL Injection Vulnerability

CVE-2026-6991 Overview

A SQL injection vulnerability has been identified in colinhacks Zod, a TypeScript-first schema validation library. The vulnerability exists in an unknown function within the file packages/zod/src/v4/core/regexes.ts, specifically in the CUID Data Type Handler component. Through manipulation of input data, an attacker can exploit this flaw to perform SQL injection attacks remotely. The exploit has been publicly disclosed, and the vendor was contacted early about this disclosure but did not respond.

Critical Impact

This SQL injection vulnerability in the Zod validation library could allow attackers to manipulate database queries, potentially leading to unauthorized data access, data modification, or data exfiltration in applications relying on Zod for input validation.

Affected Products

• colinhacks Zod up to version 4.3.6
• Applications using Zod's CUID data type validation
• Node.js/TypeScript projects with vulnerable Zod dependencies

Discovery Timeline

• April 25, 2026 - CVE-2026-6991 published to NVD
• April 29, 2026 - Last updated in NVD database

Technical Details for CVE-2026-6991

Vulnerability Analysis

This vulnerability falls under CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component), commonly referred to as injection vulnerabilities. The flaw resides in the CUID (Collision-resistant Unique Identifier) data type handler within Zod's regex processing module.

The vulnerable component fails to properly sanitize or validate input data before it is used in contexts where special characters could be interpreted as SQL commands. When applications use Zod to validate CUID-formatted strings that are subsequently used in database queries, malicious input can bypass validation and inject SQL commands.

The network-based attack vector means exploitation can occur remotely without requiring physical access to the target system. Authentication may be required depending on how the affected application implements the validation layer.

Root Cause

The root cause stems from improper input neutralization in the regexes.ts file's CUID validation logic. The regex patterns or subsequent processing do not adequately filter special characters that have meaning in SQL contexts. This allows crafted input strings that technically match CUID patterns to contain SQL injection payloads that pass validation but cause malicious behavior when the validated data reaches database operations.

Attack Vector

The attack is network-based and can be launched remotely against any application exposing endpoints that accept CUID-formatted input validated by vulnerable Zod versions. The exploitation sequence involves:

1. Identifying an application endpoint that accepts CUID input validated by Zod
2. Crafting a malicious payload that passes Zod's CUID validation while containing SQL injection syntax
3. Submitting the payload through the vulnerable endpoint
4. The malformed input passes validation and reaches database query construction
5. The injected SQL commands execute against the backend database

The vulnerability mechanism involves improper handling of special characters in the CUID validation regex within packages/zod/src/v4/core/regexes.ts. When input data passes through this handler, certain injection sequences may not be properly filtered, allowing them to reach downstream SQL query construction. For detailed technical information, refer to the VulDB Vulnerability Entry.

Detection Methods for CVE-2026-6991

Indicators of Compromise

• Unusual SQL error messages in application logs indicating malformed queries
• Unexpected database query patterns containing CUID-formatted input with special characters
• Application exceptions related to Zod validation followed by database errors
• Network traffic containing CUID-like strings with embedded SQL syntax

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect SQL injection patterns in CUID input fields
• Monitor application logs for validation bypass attempts targeting CUID data types
• Deploy database activity monitoring to detect anomalous queries originating from Zod-validated inputs
• Use static code analysis tools to identify Zod CUID validation patterns followed by database operations

Monitoring Recommendations

• Enable verbose logging for Zod validation failures and database query errors
• Set up alerts for SQL injection signature patterns in request payloads
• Monitor for unusual database access patterns following CUID-validated inputs
• Track dependency versions to identify applications using vulnerable Zod versions

How to Mitigate CVE-2026-6991

Immediate Actions Required

• Audit all applications using colinhacks Zod versions up to 4.3.6
• Implement additional input sanitization after Zod validation for database-bound data
• Apply prepared statements and parameterized queries for all database operations
• Consider implementing a Web Application Firewall to filter malicious payloads

Patch Information

At the time of disclosure, the vendor (colinhacks) was contacted but did not respond. No official patch has been confirmed. Organizations should monitor the official Zod repository for security updates and upgrade to patched versions when available. Additional context is available through the VulDB Submission and VulDB CTI Report.

Workarounds

• Implement secondary validation after Zod processing to sanitize SQL special characters
• Use parameterized queries or prepared statements for all database operations involving user input
• Deploy input filtering at the application layer to strip SQL injection payloads before Zod validation
• Consider temporarily replacing Zod CUID validation with alternative validation libraries until a patch is released

# Configuration example - Additional input sanitization layer
# Add this after Zod validation in your application pipeline

# Example Node.js middleware approach
# Ensure all CUID-validated inputs are escaped before database use
# npm install sqlstring (for MySQL) or use your ORM's escaping functions

# Monitor your Zod dependency version
npm list zod
# If version <= 4.3.6, apply workarounds immediately