CVE-2022-39173: WolfSSL Buffer Overflow Vulnerability

CVE-2022-39173 Overview

CVE-2022-39173 is a buffer overflow vulnerability in wolfSSL before version 5.5.1 that allows malicious clients to cause a denial of service during a TLS 1.3 handshake. The vulnerability is triggered when an attacker attempts to resume a previous TLS session and forces a Hello Retry Request to be processed. By sending two Client Hello messages containing duplicate cipher suites—one in the resumed session and another in response to a Hello Retry Request—an attacker can overflow a buffer and crash the affected server.

This vulnerability affects the core TLS handshake implementation in wolfSSL, a widely-used embedded SSL/TLS library deployed in IoT devices, embedded systems, and security-critical applications.

Critical Impact

Remote attackers can crash wolfSSL-based servers and applications without authentication by exploiting this buffer overflow during TLS 1.3 session resumption, leading to denial of service conditions.

Affected Products

• wolfSSL versions prior to 5.5.1
• Applications and embedded systems using vulnerable wolfSSL libraries
• IoT devices and firmware utilizing wolfSSL for TLS communications

Discovery Timeline

• 2022-09-29 - CVE-2022-39173 published to NVD
• 2025-05-20 - Last updated in NVD database

Technical Details for CVE-2022-39173

Vulnerability Analysis

This buffer overflow vulnerability (CWE-787: Out-of-bounds Write) resides in the wolfSSL TLS 1.3 handshake processing code. The flaw occurs during session resumption handling when processing Client Hello messages in conjunction with Hello Retry Request workflows.

The vulnerability requires a specific sequence of events to trigger: an attacker must first initiate a TLS session resumption attempt, then force the server to issue a Hello Retry Request. When the attacker responds with a second Client Hello containing duplicate cipher suites, the parsing logic fails to properly validate buffer boundaries, resulting in an out-of-bounds write condition.

The attack can be executed remotely over the network without requiring any authentication or user interaction. While the vulnerability does not directly lead to code execution or data exfiltration based on available information, the buffer overflow causes a crash that results in service disruption.

Root Cause

The root cause is improper bounds checking when processing cipher suite lists during TLS 1.3 handshake resumption. When duplicate cipher suites are present in successive Client Hello messages, the parsing routine does not correctly account for the accumulated data size, leading to a write operation that exceeds allocated buffer boundaries. This is classified as CWE-787 (Out-of-bounds Write).

Attack Vector

The attack exploits the TLS 1.3 session resumption mechanism through the following sequence:

1. The attacker initiates a connection to a wolfSSL server and begins a session resumption attempt
2. The attacker crafts a Client Hello message containing a list of duplicate cipher suites
3. This triggers the server to respond with a Hello Retry Request
4. The attacker sends a second Client Hello, also containing duplicate cipher suites
5. The combination of both Client Hello messages causes the buffer overflow condition
6. The server crashes, resulting in denial of service

The attack does not require authentication (PR:N), user interaction (UI:N), and can be performed remotely over the network (AV:N). According to analysis from Trail of Bits, this vulnerability was discovered through protocol fuzzing techniques.

Detection Methods for CVE-2022-39173

Indicators of Compromise

• Unexpected crashes or restarts of applications using wolfSSL for TLS communications
• Multiple TLS connection attempts from the same source with malformed or unusual Client Hello messages
• Increased frequency of TLS handshake failures followed by service crashes
• Memory corruption signatures or segmentation faults in application logs

Detection Strategies

• Monitor TLS handshake patterns for anomalous session resumption attempts with duplicate cipher suites
• Implement network intrusion detection rules to identify malformed TLS 1.3 Client Hello sequences
• Deploy application crash monitoring to detect repeated service failures correlated with incoming TLS connections
• Analyze packet captures for Client Hello messages containing unusually large or duplicated cipher suite lists

Monitoring Recommendations

• Enable detailed logging for TLS handshake events in applications using wolfSSL
• Configure alerting for unexpected application crashes or memory-related errors
• Monitor network traffic for reconnaissance patterns targeting TLS endpoints
• Implement rate limiting on TLS connection attempts from individual source addresses

How to Mitigate CVE-2022-39173

Immediate Actions Required

• Upgrade wolfSSL to version 5.5.1 or later immediately
• Identify all applications, firmware, and systems using wolfSSL and prioritize patching
• Consider temporarily disabling TLS 1.3 session resumption if immediate patching is not feasible
• Review and audit deployed IoT devices and embedded systems for vulnerable wolfSSL versions

Patch Information

wolfSSL has addressed this vulnerability in version 5.5.1. Organizations should consult the wolfSSL Security Vulnerabilities Documentation for official guidance and the wolfSSL Release Notes for upgrade information.

Additional technical details about this vulnerability are available from Packet Storm Security and the Full Disclosure Mailing List.

Workarounds

• Disable TLS 1.3 session resumption features if upgrading is not immediately possible
• Implement network-level filtering to block malformed TLS Client Hello messages
• Deploy a TLS-terminating reverse proxy or load balancer running patched software in front of vulnerable applications
• Isolate vulnerable systems from untrusted network access until patches can be applied

# Verify wolfSSL version to check for vulnerability
# wolfSSL 5.5.1 or later is required to address CVE-2022-39173
wolfssl-config --version

# If using a package manager, ensure latest version is installed
# Example for systems with wolfSSL packages:
apt list --installed | grep wolfssl