CVE-2026-23956: seroval RegExp DoS Vulnerability

CVE-2026-23956 Overview

CVE-2026-23956 is a Denial of Service vulnerability in seroval, a JavaScript library that facilitates value stringification for complex structures beyond standard JSON.stringify capabilities. The vulnerability exists in versions 1.4.0 and below, where overriding RegExp serialization with extremely large patterns can exhaust JavaScript runtime memory during deserialization. Additionally, patterns that trigger catastrophic backtracking can lead to ReDoS (Regular Expression Denial of Service).

Critical Impact

Remote attackers can cause application denial of service by crafting malicious RegExp patterns that exhaust memory or CPU resources during deserialization, potentially bringing down Node.js services that depend on seroval.

Affected Products

• seroval versions 1.4.0 and below
• Applications using seroval for JavaScript value serialization/deserialization
• Node.js services implementing seroval for complex data handling

Discovery Timeline

• 2026-01-22 - CVE CVE-2026-23956 published to NVD
• 2026-01-22 - Last updated in NVD database

Technical Details for CVE-2026-23956

Vulnerability Analysis

This vulnerability (CWE-1333: Inefficient Regular Expression Complexity) allows attackers to exploit the RegExp serialization mechanism in seroval. The library's handling of RegExp objects during deserialization does not properly validate or limit the complexity and size of regular expression patterns.

When seroval deserializes data containing crafted RegExp objects, two attack scenarios become possible. First, extremely large RegExp patterns can consume excessive memory, leading to memory exhaustion and application crashes. Second, patterns specifically designed to trigger catastrophic backtracking can cause the JavaScript regex engine to consume excessive CPU time, resulting in ReDoS conditions.

The vulnerability is particularly concerning for applications that deserialize untrusted data using seroval, as attackers can embed malicious RegExp objects within serialized payloads.

Root Cause

The root cause lies in insufficient validation of RegExp patterns during the deserialization process. Prior to version 1.4.1, seroval did not implement safeguards against oversized patterns or patterns with exponential backtracking characteristics. This allowed maliciously crafted serialized data to create RegExp objects that would consume disproportionate resources when processed by the JavaScript runtime.

Attack Vector

The attack is network-accessible and requires no authentication or user interaction. An attacker can craft a serialized payload containing a malicious RegExp pattern and send it to any application endpoint that deserializes seroval data. When the victim application deserializes the payload, the malicious RegExp is instantiated, triggering either memory exhaustion or CPU-intensive backtracking operations.

Attack scenarios include submitting malicious serialized data through API endpoints, WebSocket connections, or any other input vector where seroval deserialization occurs. For technical details on the vulnerability and its fix, see the GitHub Security Advisory.

Detection Methods for CVE-2026-23956

Indicators of Compromise

• Sudden memory spikes or out-of-memory errors in Node.js applications using seroval
• High CPU utilization with stack traces pointing to RegExp operations
• Application timeouts or unresponsiveness during data deserialization
• Error logs indicating heap memory exhaustion or maximum call stack exceeded

Detection Strategies

• Monitor application memory consumption for unusual spikes during deserialization operations
• Implement CPU usage thresholds and alerting for Node.js processes handling seroval data
• Review application dependencies using npm audit or yarn audit to identify vulnerable seroval versions
• Deploy application performance monitoring (APM) tools to detect regex-related performance anomalies

Monitoring Recommendations

• Enable detailed logging for seroval deserialization operations to capture payload characteristics
• Configure resource limits and timeouts for deserialization processes to prevent complete service disruption
• Implement rate limiting on endpoints that accept serialized data to reduce attack surface
• Use SentinelOne Singularity Platform to monitor for resource exhaustion patterns and DoS indicators

How to Mitigate CVE-2026-23956

Immediate Actions Required

• Upgrade seroval to version 1.4.1 or later immediately
• Audit all applications using seroval to identify affected deployments
• Implement input validation to reject or sanitize serialized data from untrusted sources
• Consider implementing timeout mechanisms for deserialization operations as a defense-in-depth measure

Patch Information

The vulnerability has been addressed in seroval version 1.4.1. The fix implements proper validation and restrictions on RegExp serialization to prevent both memory exhaustion and ReDoS attacks. The patch can be reviewed at the GitHub commit.

To update, run:

npm update seroval
# or
yarn upgrade seroval

Workarounds

• Implement input size limits on serialized data before passing to seroval deserialization
• Add timeout wrappers around deserialization calls to terminate long-running operations
• Sanitize or reject RegExp objects from untrusted serialized data before processing
• Deploy Web Application Firewall (WAF) rules to filter potentially malicious serialized payloads

# Verify seroval version after update
npm list seroval
# Expected output should show version 1.4.1 or higher

# Check for vulnerable dependencies in your project
npm audit --audit-level=high