CVE-2019-20922
📋 TL;DR
This CVE describes a Regular Expression Denial of Service (ReDoS) vulnerability in Handlebars templating engine versions before 4.4.5. Attackers can craft malicious templates that force the parser into an endless loop, consuming excessive CPU resources and potentially causing service disruption. This affects any application using vulnerable Handlebars versions for template processing.
💻 Affected Systems
- handlebars.js
- Any application using Handlebars templating engine
📦 What is this software?
Handlebars by Handlebarsjs
⚠️ Risk & Real-World Impact
Worst Case
Complete service unavailability due to resource exhaustion, potentially affecting multiple services on shared infrastructure.
Likely Case
Degraded performance or temporary service disruption for applications processing untrusted templates.
If Mitigated
Minimal impact with proper input validation and resource limits in place.
🎯 Exploit Status
Exploitation requires ability to submit crafted templates to vulnerable endpoints. Proof-of-concept examples are publicly available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.4.5 and later
Vendor Advisory: https://github.com/handlebars-lang/handlebars.js/commit/8d5530ee2c3ea9f0aee3fde310b9f36887d00b8b
Restart Required: Yes
Instructions:
1. Update Handlebars dependency to version 4.4.5 or later. 2. For npm: 'npm update handlebars'. 3. For yarn: 'yarn upgrade handlebars'. 4. Restart affected applications.
🔧 Temporary Workarounds
Input Validation and Sanitization
allImplement strict validation and sanitization of template inputs to prevent malicious patterns.
Resource Limiting
allImplement CPU timeouts and resource limits for template processing operations.
🧯 If You Can't Patch
- Implement strict input validation to reject complex template patterns
- Deploy resource monitoring and alerting for abnormal CPU usage patterns
🔍 How to Verify
Check if Vulnerable:
Check package.json or run 'npm list handlebars' to see installed version.Check Version:
npm list handlebars | grep handlebarsVerify Fix Applied:
Verify installed version is 4.4.5 or later using 'npm list handlebars' or check package.json.📡 Detection & Monitoring
Log Indicators:
- Unusually high CPU usage during template processing
- Long-running template compilation operations
Network Indicators:
- Repeated template submission patterns
- Unusually large template payloads
SIEM Query:
source=application_logs AND ("template processing" OR "handlebars") AND (cpu_usage>90 OR duration>10s)🔗 References
- https://github.com/handlebars-lang/handlebars.js/commit/8d5530ee2c3ea9f0aee3fde310b9f36887d00b8b
- https://snyk.io/vuln/SNYK-JS-HANDLEBARS-480388
- https://www.npmjs.com/advisories/1300
- https://github.com/handlebars-lang/handlebars.js/commit/8d5530ee2c3ea9f0aee3fde310b9f36887d00b8b
- https://snyk.io/vuln/SNYK-JS-HANDLEBARS-480388
- https://www.npmjs.com/advisories/1300
