CVE-2024-5814 Overview
CVE-2024-5814 affects the wolfSSL cryptographic library and enables a ciphersuite confusion attack against TLS 1.3 clients that support protocol downgrade. A malicious TLS 1.2 server can force a downgrade-capable TLS 1.3 client to accept a ciphersuite it never advertised or agreed to, yet still complete a successful handshake. The root cause is incomplete parsing of the ServerHello message: the client processes extensions but skips full validation of the negotiated ciphersuite. The vulnerability is classified under [CWE-284: Improper Access Control] and requires user interaction from an active network-position attacker. Research documenting the flaw was published in IACR TCHES 2024.
Critical Impact
A network-positioned attacker operating a malicious TLS 1.2 server can steer a wolfSSL TLS 1.3 client into a ciphersuite of the attacker's choosing, weakening the confidentiality guarantees of the established session.
Affected Products
- wolfSSL library (TLS 1.3 client builds with downgrade support enabled)
- Applications and embedded devices linking against affected wolfSSL versions
- IoT and constrained systems relying on wolfSSL for TLS termination
Discovery Timeline
- 2024-08-27 - CVE-2024-5814 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2024-5814
Vulnerability Analysis
The vulnerability is a TLS protocol implementation flaw in wolfSSL's client-side handshake logic. TLS 1.3 clients that retain TLS 1.2 compatibility must validate every field of the ServerHello, including the selected ciphersuite, against the ciphersuites offered in the ClientHello. wolfSSL's client parsed the extensions but did not fully verify the cipher_suite field returned by the server.
As a result, a malicious TLS 1.2 server can respond with a ciphersuite that was never present in the client's offered list. The client proceeds with key derivation and finishes the handshake using an unnegotiated algorithm. This weakens the integrity of the negotiation and can be leveraged to steer sessions toward weaker cryptographic primitives supported by the client's implementation but not intended for use in that connection.
The issue is categorized as a cryptographic and protocol implementation defect [CWE-284] and closely aligns with SSL/TLS Vulnerability and Man-in-the-Middle attack classes. EPSS data places exploitation probability at 0.466% (38.5 percentile).
Root Cause
The ServerHello handler skipped full validation of server-selected parameters. The client trusted the server's chosen ciphersuite without cross-checking it against the list transmitted in the ClientHello, violating RFC 8446 Section 4.1.3 requirements.
Attack Vector
An attacker must control or impersonate a TLS server that the victim client attempts to connect to. This typically requires either operating a malicious endpoint or holding an on-path position that allows redirection to an attacker-controlled server. Once the client initiates a TLS 1.3 handshake with downgrade capability enabled, the malicious server responds as TLS 1.2 and injects an arbitrary ciphersuite into the ServerHello. The wolfSSL client accepts it and completes the handshake, producing a session negotiated on terms the client never agreed to.
No exploitation code example is published for this issue. See the wolfSSL ChangeLog for fix references and the academic disclosure for the underlying research.
Detection Methods for CVE-2024-5814
Indicators of Compromise
- TLS sessions where the server-selected ciphersuite in ServerHello is not present in the corresponding ClientHello offered list.
- Unexpected TLS 1.2 downgrades on clients that were configured to prefer TLS 1.3.
- Handshakes to untrusted or newly observed server endpoints negotiating legacy or weaker ciphersuites.
Detection Strategies
- Inspect TLS handshake telemetry at network sensors and correlate ClientHello ciphersuite lists with the final ServerHello selection.
- Identify wolfSSL-linked binaries and firmware images in the environment and inventory their versions against the vendor changelog.
- Alert on outbound TLS 1.2 handshakes originating from applications known to support TLS 1.3.
Monitoring Recommendations
- Ingest TLS metadata (JA3/JA4, negotiated version, negotiated ciphersuite) into your SIEM for continuous baselining.
- Track anomalies in ciphersuite selection per client application and flag deviations from historical norms.
- Monitor connections to non-corporate or newly registered domains from IoT and embedded devices running wolfSSL.
How to Mitigate CVE-2024-5814
Immediate Actions Required
- Upgrade wolfSSL to the fixed release referenced in the wolfSSL ChangeLog.
- Rebuild and redeploy all applications, firmware, and containers statically linked against vulnerable wolfSSL versions.
- Audit endpoints and IoT fleets to identify wolfSSL consumers and prioritize those exposed to untrusted networks.
Patch Information
wolfSSL corrected the ServerHello parsing path so the client fully validates the server-selected ciphersuite against the offered list before continuing the handshake. Consult the vendor ChangeLog for the specific fixed version and commit references.
Workarounds
- Disable TLS 1.2 downgrade support in wolfSSL build configurations where TLS 1.3 is sufficient for all peers.
- Enforce strict ciphersuite allowlists at the application layer so unexpected server selections cause connection abort.
- Restrict client connectivity to known, authenticated servers via certificate pinning or mutual TLS.
# Configuration example: build wolfSSL without TLS 1.2 fallback
./configure --enable-tls13 --disable-tlsv12 --enable-harden
make && sudo make install
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
