CVE-2026-26021
📋 TL;DR
CVE-2026-26021 is a prototype pollution vulnerability in the npm package set-in that allows attackers to modify Object.prototype through crafted array inputs. This affects applications using set-in versions 2.0.1 through 2.0.4 for nested object manipulation. Successful exploitation could lead to denial of service, remote code execution, or privilege escalation depending on application context.
💻 Affected Systems
- set-in npm package
📦 What is this software?
Set In by Set In Project
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data exfiltration, and lateral movement within the network.
Likely Case
Application crashes, denial of service, or unauthorized modification of application behavior leading to data integrity issues.
If Mitigated
Limited impact with proper input validation and sandboxing, potentially causing only application instability.
🎯 Exploit Status
Exploitation requires understanding of prototype pollution techniques and ability to control input to set-in functions.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.0.5
Vendor Advisory: https://github.com/ahdinosaur/set-in/security/advisories/GHSA-2c4m-g7rx-63q7
Restart Required: No
Instructions:
1. Update package.json to require set-in version 2.0.5 or higher. 2. Run 'npm update set-in' or 'yarn upgrade set-in'. 3. Test application functionality after update.
🔧 Temporary Workarounds
Input validation wrapper
allWrap set-in calls with validation to reject arrays containing prototype pollution patterns
// Example validation function
function safeSetIn(obj, path, value) {
if (Array.isArray(path) && path.some(key => key === '__proto__' || key === 'constructor' || key === 'prototype')) {
throw new Error('Invalid path for set-in');
}
return setIn(obj, path, value);
}
🧯 If You Can't Patch
- Implement strict input validation for all user-controlled data passed to set-in functions
- Use object property whitelisting and avoid passing user-controlled arrays to set-in
🔍 How to Verify
Check if Vulnerable:
Check package.json or package-lock.json for set-in version between 2.0.1 and 2.0.4Check Version:
npm list set-in | grep set-inVerify Fix Applied:
Verify set-in version is 2.0.5 or higher in package.json and test with known malicious inputs📡 Detection & Monitoring
Log Indicators:
- Unusual application crashes, unexpected object property modifications, or prototype pollution attempts in logs
Network Indicators:
- Unusual API calls with array parameters containing suspicious keys like '__proto__' or 'constructor'
SIEM Query:
source="application_logs" AND ("set-in" OR "prototype pollution" OR "__proto__")