CVE-2024-30166: Arm Mbed TLS Information Disclosure Flaw

CVE-2024-30166 Overview

CVE-2024-30166 is a critical stack buffer over-read vulnerability affecting Arm Mbed TLS versions 3.3.0 through 3.5.2. The vulnerability exists in the TLS 1.3 server implementation and can be triggered by a malicious client sending a specially crafted TLS 3.1 ClientHello message. Successful exploitation allows an attacker to cause information disclosure (reading up to 256 bytes from the stack) or denial of service conditions on vulnerable TLS servers.

Mbed TLS is a widely deployed open-source cryptographic library used in embedded systems, IoT devices, and various applications requiring secure communications. This vulnerability poses significant risk to any TLS 1.3 server implementation built on affected versions.

Critical Impact

Remote attackers can exploit this vulnerability over the network without authentication to leak sensitive memory contents or crash TLS 1.3 servers, potentially exposing cryptographic keys or other sensitive data stored on the stack.

Affected Products

• Arm Mbed TLS versions 3.3.0 through 3.5.2
• TLS 1.3 server implementations using affected Mbed TLS versions
• Embedded systems and IoT devices utilizing vulnerable Mbed TLS libraries

Discovery Timeline

• 2024-04-03 - CVE-2024-30166 published to NVD
• 2025-06-27 - Last updated in NVD database

Technical Details for CVE-2024-30166

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), specifically manifesting as a stack buffer over-read condition. The flaw resides in how Mbed TLS 3.x handles incoming ClientHello messages during TLS 1.3 handshake processing.

When a TLS 1.3 server receives a malformed ClientHello message that indicates TLS 3.1 protocol version, the parsing logic fails to properly validate buffer boundaries before reading data. This allows the read operation to exceed the intended buffer limits by up to 256 bytes, accessing adjacent stack memory.

The vulnerability is remotely exploitable over the network, requires no user interaction, and can be triggered without any authentication or special privileges. An attacker simply needs network access to a vulnerable TLS 1.3 server endpoint.

Root Cause

The root cause stems from improper input validation in the ClientHello parsing routines within the TLS 1.3 server implementation. When processing version negotiation fields, the code fails to enforce proper bounds checking when handling unexpected or malformed protocol version indicators. The TLS 3.1 version field triggers a code path that reads beyond allocated stack buffer boundaries.

Attack Vector

The attack vector is network-based, targeting TLS 1.3 servers running vulnerable Mbed TLS versions. An attacker establishes a connection to the target server and sends a specially crafted ClientHello message containing a TLS 3.1 version indicator. The malformed message triggers the over-read condition during handshake processing.

The attack can result in two outcomes:

1. Information Disclosure: Leaked stack contents may include sensitive data such as cryptographic material, session tokens, or other confidential information residing in adjacent stack memory
2. Denial of Service: The over-read may cause the server process to crash, disrupting availability for legitimate clients

No specific exploitation code is publicly available for this vulnerability. The attack involves sending a malformed TLS ClientHello message with crafted version negotiation parameters to trigger the stack buffer over-read during server-side handshake processing. For technical implementation details, refer to the Mbed TLS Security Advisory.

Detection Methods for CVE-2024-30166

Indicators of Compromise

• Unusual TLS handshake failures or server crashes during ClientHello processing
• Abnormal ClientHello messages with unexpected TLS version indicators (TLS 3.1)
• Increased memory access violations or segmentation faults in TLS server processes
• Network traffic containing malformed TLS handshake packets targeting port 443 or other TLS-enabled services

Detection Strategies

• Monitor TLS server logs for repeated handshake failures with unusual error codes related to version parsing
• Deploy network intrusion detection signatures to identify malformed ClientHello packets with TLS 3.1 version fields
• Implement application-level monitoring for unexpected process terminations in TLS server components
• Use vulnerability scanning tools to identify systems running Mbed TLS versions 3.3.0 through 3.5.2

Monitoring Recommendations

• Enable verbose TLS handshake logging on servers running potentially vulnerable Mbed TLS versions
• Configure alerting for unusual patterns of failed TLS connections from single source IPs
• Monitor system stability metrics for TLS server processes including crash rates and memory errors
• Implement network traffic analysis to detect anomalous ClientHello message structures

How to Mitigate CVE-2024-30166

Immediate Actions Required

• Upgrade Mbed TLS to version 3.6.0 or later immediately on all affected systems
• Inventory all systems, applications, and embedded devices using Mbed TLS 3.x libraries
• Prioritize patching for internet-facing TLS 1.3 servers
• Review and audit third-party software dependencies that may bundle affected Mbed TLS versions

Patch Information

Arm has addressed this vulnerability in Mbed TLS version 3.6.0. Organizations should upgrade to this version or later to remediate CVE-2024-30166. The fix is available through the GitHub Mbed TLS Release v3.6.0.

For detailed security advisory information, consult the Mbed TLS Security Advisory Updates.

Workarounds

• If immediate patching is not possible, consider temporarily disabling TLS 1.3 support and falling back to TLS 1.2 on affected servers
• Implement network-level filtering to block or rate-limit suspicious TLS handshake attempts
• Place vulnerable servers behind a TLS-terminating reverse proxy running patched software
• Restrict network access to TLS servers using firewall rules to limit exposure to trusted clients only

# Verify Mbed TLS version in your environment
# Check installed version (method varies by system)
grep -r "MBEDTLS_VERSION_STRING" /path/to/mbedtls/include/

# After upgrading, verify the new version is 3.6.0 or later
# Rebuild applications linking against Mbed TLS
make clean && make all

# Restart services using Mbed TLS after patching
systemctl restart your-tls-service