CVE-2020-36423
📋 TL;DR
This vulnerability in Arm Mbed TLS allows a remote attacker to recover plaintext from encrypted communications due to an incomplete Lucky 13 countermeasure when hardware acceleration is used. It affects systems using Mbed TLS versions before 2.23.0 with hardware acceleration enabled. The vulnerability enables decryption of sensitive data transmitted over TLS connections.
💻 Affected Systems
- Arm Mbed TLS
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of encrypted communications, allowing attackers to decrypt sensitive data including credentials, session tokens, and confidential information transmitted over TLS.
Likely Case
Partial plaintext recovery from encrypted sessions, potentially exposing sensitive application data or authentication credentials.
If Mitigated
Minimal impact if proper patching is applied and hardware acceleration is disabled or properly configured.
🎯 Exploit Status
Exploitation requires network access to TLS endpoints and ability to observe encrypted traffic. The Lucky 13 attack is well-documented and has been weaponized in other contexts.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.23.0 or later
Vendor Advisory: https://github.com/ARMmbed/mbedtls/releases/tag/v2.23.0
Restart Required: Yes
Instructions:
1. Update Mbed TLS to version 2.23.0 or later. 2. Recompile applications using Mbed TLS. 3. Restart affected services. 4. Verify the update was successful.
🔧 Temporary Workarounds
Disable Hardware Acceleration
allDisable hardware acceleration in Mbed TLS configuration to avoid the vulnerable code path
Configure MBEDTLS_HAVE_TIME and MBEDTLS_HAVE_TIME_DATE to 0 in mbedtls_config.h
Set MBEDTLS_TIMING_C to 0 if not needed
🧯 If You Can't Patch
- Implement network segmentation to limit exposure of vulnerable systems
- Use additional encryption layers (e.g., VPN, application-layer encryption) for sensitive data
🔍 How to Verify
Check if Vulnerable:
Check Mbed TLS version: mbedtls_version_get_string() or check library version in system packagesCheck Version:
ldd <application> | grep mbedtls or check package manager (apt list --installed | grep mbedtls)Verify Fix Applied:
Verify Mbed TLS version is 2.23.0 or later and hardware acceleration configuration is reviewed📡 Detection & Monitoring
Log Indicators:
- Unusual decryption errors
- TLS handshake anomalies
- Increased failed connection attempts
Network Indicators:
- Unusual traffic patterns to TLS endpoints
- Multiple connection attempts with timing variations
SIEM Query:
source="*tls*" AND (error OR failed OR anomaly) AND (handshake OR decrypt)🔗 References
- https://bugs.gentoo.org/730752
- https://github.com/ARMmbed/mbedtls/releases/tag/v2.16.7
- https://github.com/ARMmbed/mbedtls/releases/tag/v2.23.0
- https://lists.debian.org/debian-lts-announce/2022/12/msg00036.html
- https://bugs.gentoo.org/730752
- https://github.com/ARMmbed/mbedtls/releases/tag/v2.16.7
- https://github.com/ARMmbed/mbedtls/releases/tag/v2.23.0
- https://lists.debian.org/debian-lts-announce/2022/12/msg00036.html
