CVE-2026-3230: wolfSSL TLS 1.3 Information Disclosure Flaw

CVE-2026-3230 Overview

A cryptographic vulnerability exists in wolfSSL's TLS 1.3 client implementation that fails to properly enforce required steps during the HelloRetryRequest handshake sequence. The flaw allows an attacker to compromise the confidentiality of TLS-protected communications by sending a crafted HelloRetryRequest followed by a ServerHello message that omits the required key_share extension. This results in derivation of predictable traffic secrets from (EC)DHE shared secret, potentially exposing encrypted communications to interception.

Critical Impact

TLS 1.3 confidentiality can be compromised through manipulation of the HelloRetryRequest handshake, leading to derivation of predictable traffic secrets and potential exposure of encrypted communications.

Affected Products

• wolfSSL TLS 1.3 client implementations (versions prior to patch)

Discovery Timeline

• 2026-03-19 - CVE CVE-2026-3230 published to NVD
• 2026-03-19 - Last updated in NVD database

Technical Details for CVE-2026-3230

Vulnerability Analysis

This vulnerability stems from improper input validation (CWE-20) in the wolfSSL TLS 1.3 client's HelloRetryRequest handling logic. During a standard TLS 1.3 handshake, when a server sends a HelloRetryRequest message, the client is expected to generate a new key_share extension with different cryptographic parameters. The subsequent ServerHello from the server must also contain a key_share extension for proper (EC)DHE key exchange.

The vulnerability occurs because the wolfSSL client does not properly validate that the ServerHello message following a HelloRetryRequest contains the mandatory key_share extension. When this extension is missing, the client proceeds with key derivation using incomplete or predictable input material, resulting in traffic secrets that can be computed by an attacker who controls the server or can perform a man-in-the-middle attack.

Importantly, this vulnerability does not affect the client's authentication of the server during TLS handshakes, meaning certificate validation and server identity verification remain intact.

Root Cause

The root cause is a missing validation step in the TLS 1.3 client state machine. According to RFC 8446, when a client receives a HelloRetryRequest, the subsequent ServerHello must contain a key_share extension. The wolfSSL implementation fails to enforce this requirement, allowing the handshake to proceed with a malformed ServerHello. This represents a deviation from the TLS 1.3 specification that creates a window for cryptographic attack.

Attack Vector

An attacker positioned as a malicious server or performing a man-in-the-middle attack can exploit this vulnerability by:

1. Initiating a TLS 1.3 handshake with a vulnerable wolfSSL client
2. Sending a crafted HelloRetryRequest that triggers key share renegotiation
3. Following up with a ServerHello message that deliberately omits the key_share extension
4. The client proceeds with key derivation using predictable or incomplete shared secret material
5. The attacker, knowing the predictable derivation inputs, can compute the same traffic secrets and decrypt subsequent communications

The attack requires network access and the ability to intercept or control server responses. While the technical complexity is high and requires privileged network position, successful exploitation compromises the fundamental confidentiality guarantees of TLS.

Detection Methods for CVE-2026-3230

Indicators of Compromise

• TLS 1.3 connections completing successfully despite malformed ServerHello messages missing key_share extensions
• Unusual HelloRetryRequest sequences in TLS handshake logs
• Network traffic anomalies suggesting TLS downgrade or manipulation attempts

Detection Strategies

• Monitor TLS handshake sequences for HelloRetryRequest messages followed by ServerHello packets that may be malformed
• Implement deep packet inspection to validate TLS 1.3 handshake conformance with RFC 8446 requirements
• Deploy intrusion detection rules targeting anomalous TLS 1.3 handshake patterns
• Audit applications using wolfSSL to identify vulnerable deployments

Monitoring Recommendations

• Enable verbose TLS handshake logging in wolfSSL-based applications to capture HelloRetryRequest sequences
• Implement network-level monitoring for TLS 1.3 sessions exhibiting unusual key exchange patterns
• Configure SIEM rules to alert on TLS handshake anomalies from critical systems
• Periodically audit TLS implementations for compliance with cryptographic standards

How to Mitigate CVE-2026-3230

Immediate Actions Required

• Identify all applications and systems using wolfSSL for TLS 1.3 client connections
• Apply the patch referenced in the GitHub Pull Request for wolfSSL
• Prioritize patching for systems handling sensitive data or operating in untrusted network environments
• Review network architecture to ensure TLS traffic traverses trusted paths where possible

Patch Information

The wolfSSL development team has addressed this vulnerability through a code fix that properly validates the presence of the key_share extension in ServerHello messages following HelloRetryRequest sequences. The patch is available via the GitHub Pull Request for wolfSSL. Organizations should update to a version of wolfSSL that includes this fix.

Workarounds

• Where possible, configure TLS clients to disable HelloRetryRequest handling if the feature is not required for your deployment
• Implement network segmentation to reduce exposure of vulnerable clients to untrusted servers
• Use network security controls to monitor and restrict outbound TLS connections to known-good servers
• Consider using additional transport encryption layers (e.g., VPN) for sensitive communications until patching is complete