CVE-2021-4110
📋 TL;DR
CVE-2021-4110 is a NULL pointer dereference vulnerability in mruby, a lightweight implementation of the Ruby programming language. This vulnerability allows attackers to cause denial of service (DoS) by crashing applications that use vulnerable mruby versions. Any system running affected mruby versions is potentially vulnerable.
💻 Affected Systems
- mruby
📦 What is this software?
Mruby by Mruby
⚠️ Risk & Real-World Impact
Worst Case
Complete application crash leading to denial of service, potentially affecting availability of services that depend on mruby.
Likely Case
Application instability or crashes when processing malicious input, resulting in temporary service disruption.
If Mitigated
Minimal impact with proper input validation and error handling in place, though the underlying vulnerability remains.
🎯 Exploit Status
Proof of concept available through huntr.dev bounty. Exploitation requires triggering the NULL pointer dereference through crafted input.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Commit f5e10c5a79a17939af763b1dcf5232ce47e24a34 and later
Vendor Advisory: https://github.com/mruby/mruby/commit/f5e10c5a79a17939af763b1dcf5232ce47e24a34
Restart Required: Yes
Instructions:
1. Update mruby to commit f5e10c5a79a17939af763b1dcf5232ce47e24a34 or later. 2. Rebuild any applications using mruby. 3. Restart affected services.
🔧 Temporary Workarounds
Input Validation
allImplement strict input validation to prevent malicious input from reaching vulnerable mruby code paths.
Error Handling
allAdd robust error handling around mruby calls to catch and handle crashes gracefully.
🧯 If You Can't Patch
- Isolate affected systems from untrusted networks and inputs.
- Implement monitoring and alerting for application crashes related to mruby.
🔍 How to Verify
Check if Vulnerable:
Check mruby version or commit hash. If using commit prior to f5e10c5a79a17939af763b1dcf5232ce47e24a34, system is vulnerable.Check Version:
Check mruby source or build configuration for commit hash. For compiled applications, check with vendor documentation.Verify Fix Applied:
Verify mruby is at commit f5e10c5a79a17939af763b1dcf5232ce47e24a34 or later. Test with known PoC input to ensure no crash occurs.📡 Detection & Monitoring
Log Indicators:
- Application crashes, segmentation faults, or abnormal terminations in mruby-related processes.
Network Indicators:
- Unusual input patterns or repeated requests causing service disruption.
SIEM Query:
Search for 'segmentation fault', 'SIGSEGV', or abnormal process termination in application logs.