CVE-2023-30847
📋 TL;DR
CVE-2023-30847 is a memory corruption vulnerability in H2O HTTP server's reverse proxy handler that occurs when processing certain invalid HTTP requests. This can cause crashes or information disclosure to backend servers. Affected users are those running H2O versions 2.3.0-beta2 and earlier with reverse proxy functionality enabled.
💻 Affected Systems
- H2O HTTP Server
📦 What is this software?
H2o by Dena
H2o by Dena
H2o by Dena
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, though this is less likely than information disclosure or denial of service.
Likely Case
Server crashes causing denial of service, or memory content leakage to backend servers potentially exposing sensitive data.
If Mitigated
Limited impact with proper network segmentation and reverse proxy isolation, though crashes could still affect availability.
🎯 Exploit Status
Exploitation requires crafting specific invalid HTTP requests that trigger the uninitialized pointer condition. No public exploit code has been identified.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Commit f010336 or later from master branch
Vendor Advisory: https://github.com/h2o/h2o/security/advisories/GHSA-p5hj-phwj-hrvx
Restart Required: Yes
Instructions:
1. Update H2O to commit f010336 or later from the master branch. 2. Rebuild from source if using source installation. 3. Restart the H2O service. 4. Verify the fix by checking the commit hash matches f010336 or later.
🔧 Temporary Workarounds
Disable Reverse Proxy
allTemporarily disable reverse proxy functionality if not required
Modify H2O configuration to remove reverse proxy directives
Request Filtering
allImplement WAF or load balancer to filter malformed HTTP requests
🧯 If You Can't Patch
- Implement network segmentation to isolate H2O servers from sensitive backend systems
- Deploy Web Application Firewall (WAF) with rules to detect and block malformed HTTP requests
🔍 How to Verify
Check if Vulnerable:
Check H2O version: if running version 2.3.0-beta2 or earlier, and reverse proxy is enabled, the system is vulnerable.Check Version:
Check H2O configuration files for version information or examine build/installation logsVerify Fix Applied:
Verify the installed commit hash is f010336 or later: check build logs or run 'h2o --version' if available.📡 Detection & Monitoring
Log Indicators:
- Unexpected server crashes
- Error messages related to reverse proxy URL building
- Memory access violation logs
Network Indicators:
- Malformed HTTP requests to reverse proxy endpoints
- Unusual traffic patterns to backend servers
SIEM Query:
source="h2o" AND (error OR crash OR "uninitialized" OR "reverse proxy")🔗 References
- https://github.com/h2o/h2o/commit/f010336bab162839df43d9e87570897466c97e33
- https://github.com/h2o/h2o/pull/3229
- https://github.com/h2o/h2o/security/advisories/GHSA-p5hj-phwj-hrvx
- https://github.com/h2o/h2o/commit/f010336bab162839df43d9e87570897466c97e33
- https://github.com/h2o/h2o/pull/3229
- https://github.com/h2o/h2o/security/advisories/GHSA-p5hj-phwj-hrvx
