CVE-2021-37848
📋 TL;DR
This vulnerability in Pengutronix barebox bootloader leaks timing information during password hash comparison, allowing attackers to perform timing attacks. It affects all barebox versions through 2021.07.0. Systems using barebox for boot authentication are vulnerable to password brute-forcing.
💻 Affected Systems
- Pengutronix barebox
📦 What is this software?
Barebox by Pengutronix
⚠️ Risk & Real-World Impact
Worst Case
Attackers could brute-force bootloader passwords offline using timing side-channels, potentially gaining unauthorized access to boot process and compromising system integrity.
Likely Case
Local attackers with physical or console access could perform timing attacks to deduce password hashes, though successful exploitation requires specific conditions.
If Mitigated
With proper physical security and console access controls, risk is significantly reduced as attackers need proximity to target systems.
🎯 Exploit Status
Exploitation requires ability to measure timing differences during password comparison; proof-of-concept demonstrates timing attack methodology.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in commit a3337563c705bc8e0cf32f910b3e9e3c43d962ff and later versions
Vendor Advisory: https://github.com/saschahauer/barebox/commit/a3337563c705bc8e0cf32f910b3e9e3c43d962ff
Restart Required: Yes
Instructions:
1. Update barebox to version after 2021.07.0 or apply commit a3337563c705bc8e0cf32f910b3e9e3c43d962ff. 2. Recompile barebox with fixed code. 3. Flash updated bootloader to affected devices. 4. Reboot system to load patched bootloader.
🔧 Temporary Workarounds
Disable barebox password authentication
linuxRemove password protection from barebox bootloader if not required
Modify barebox configuration to remove CONFIG_PASSWORD option
Recompile and redeploy barebox without password support
Implement physical security controls
allRestrict physical and console access to prevent timing measurement attacks
🧯 If You Can't Patch
- Implement strict physical access controls to prevent attackers from measuring timing
- Monitor console access logs for suspicious authentication attempts
🔍 How to Verify
Check if Vulnerable:
Check barebox version: 'cat /proc/version' or examine bootloader version during startup. If version is 2021.07.0 or earlier, system is vulnerable.Check Version:
barebox -v || cat /proc/version || check bootloader version during system startupVerify Fix Applied:
Verify barebox version is after 2021.07.0 or contains commit a3337563c705bc8e0cf32f910b3e9e3c43d962ff in git history.📡 Detection & Monitoring
Log Indicators:
- Multiple failed authentication attempts with timing patterns
- Unusual console access outside maintenance windows
Network Indicators:
- Not applicable - local bootloader vulnerability
SIEM Query:
source="console_logs" AND "authentication failed" | stats count by src_ip, time_interval | where count > threshold🔗 References
- https://gist.github.com/gquere/816dfadbad98745090034100a8a651eb
- https://github.com/saschahauer/barebox/commit/a3337563c705bc8e0cf32f910b3e9e3c43d962ff
- https://gist.github.com/gquere/816dfadbad98745090034100a8a651eb
- https://github.com/saschahauer/barebox/commit/a3337563c705bc8e0cf32f910b3e9e3c43d962ff
