CVE-2021-29935
📋 TL;DR
This vulnerability in the Rocket web framework for Rust allows use-after-free memory corruption when user-provided functions panic during URI formatting. Attackers could potentially execute arbitrary code or crash applications. Any Rust application using Rocket versions before 0.4.7 is affected.
💻 Affected Systems
- Rocket web framework for Rust
📦 What is this software?
Rocket by Rocket
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, or service disruption
Likely Case
Application crash causing denial of service, potentially leading to memory corruption that could be leveraged for further exploitation
If Mitigated
Limited impact with proper panic handling and memory safety controls, though crashes may still occur
🎯 Exploit Status
Exploitation requires triggering a panic in user-provided URI formatting functions, which may be difficult without application-specific knowledge
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.4.7 and later
Vendor Advisory: https://rustsec.org/advisories/RUSTSEC-2021-0044.html
Restart Required: Yes
Instructions:
1. Update Cargo.toml to specify rocket = "^0.4.7"
2. Run 'cargo update rocket'
3. Rebuild and redeploy your application
4. Restart all affected services
🔧 Temporary Workarounds
Avoid custom URI formatters
allRemove or disable any custom user-provided functions in uri::Formatter usage
Review and modify Rocket application code to avoid custom URI formatting functions
Implement panic handlers
allAdd global panic handlers that prevent memory corruption on panic
Add std::panic::set_hook() with proper memory safety in main()
🧯 If You Can't Patch
- Implement strict input validation for all URI formatting operations
- Deploy application behind a WAF with memory corruption protection rules
🔍 How to Verify
Check if Vulnerable:
Check Cargo.lock or Cargo.toml for rocket version <0.4.7Check Version:
grep -A2 'name = "rocket"' Cargo.lock | grep versionVerify Fix Applied:
Verify rocket version is >=0.4.7 in Cargo.lock and test URI formatting with panic scenarios📡 Detection & Monitoring
Log Indicators:
- Application crashes with panic messages related to URI formatting
- Memory access violation errors in application logs
Network Indicators:
- HTTP requests with malformed URIs causing application termination
SIEM Query:
source="application.logs" AND ("panic" OR "use-after-free" OR "uri::Formatter")