CVE-2026-6325: WolfSSL Out-of-Bounds Write in SetSuitesHashSigAlgo

Technical summary

CVE-2026-6325 is an out-of-bounds write vulnerability (CWE-787) in the SetSuitesHashSigAlgo function within WolfSSL. The function fails to properly validate the size of an incoming signature algorithms list before writing it into a fixed-size buffer on the stack or heap. An attacker can craft a TLS ClientHello or ServerHello message containing an oversized signature_algorithms extension that exceeds the buffer's capacity, causing the write operation to overflow into adjacent memory regions. The vulnerability is reachable without authentication during the initial TLS handshake negotiation phase.

Business impact

Exploiting this vulnerability could lead to denial of service through application crashes or memory corruption that destabilizes the TLS service. In certain configurations, successful heap corruption might enable integrity attacks that compromise data in flight or modify application state. Organizations using WolfSSL in TLS server or client roles—particularly in embedded systems, IoT devices, or lightweight cryptographic deployments—face service disruption risk. The network-accessible nature and lack of authentication requirement elevate the threat profile for internet-facing deployments.

Affected systems

WolfSSL library versions prior to the security update are affected. WolfSSL is widely embedded in networking stacks, VPN clients, IoT firmware, and embedded TLS implementations. Any application linking against a vulnerable version of WolfSSL and accepting TLS connections (either as server or client) is potentially exposed. Verify your specific version against the WolfSSL security advisory to determine if patching is necessary.

Exploitability

This vulnerability has a low barrier to exploitation. An unauthenticated remote attacker can trigger the flaw by sending a malformed TLS handshake message over the network; no special conditions, user interaction, or authentication are required. The attack surface is the TLS handshake itself, which is automatically performed whenever clients connect. Proof-of-concept development would be straightforward for an attacker with TLS protocol knowledge. The vulnerability is not yet listed in CISA's Known Exploited Vulnerabilities catalog, but the simplicity of triggering it makes active exploitation a realistic near-term concern.

Remediation

Apply the security patch released by WolfSSL for CVE-2026-6325 immediately. The patch adds proper bounds checking to the signature algorithms list processing. Verify the patched version number against the official WolfSSL advisory. Until patching is feasible, consider network segmentation to limit exposure of affected TLS services, though this does not eliminate the risk for intentionally exposed services.

Patch guidance

Consult the official WolfSSL security advisory for the specific patched version number and release date. Update your WolfSSL library to the version containing the fix, then rebuild and redeploy affected applications. Test the updated version in a staging environment to ensure compatibility with your TLS implementation before production rollout. If you are using WolfSSL via a third-party vendor or embedded device firmware, contact your vendor for patched firmware or image availability.

Detection guidance

Look for TLS ClientHello or ServerHello packets with unusually large signature_algorithms extensions (significantly exceeding typical size of ~30–50 bytes). Network IDS/IPS signatures can flag malformed or oversized extension fields during TLS handshake capture. Application-level monitoring should track WolfSSL library crashes or segmentation faults correlated with inbound TLS connections. Enable verbose TLS logging if available to detect parsing errors on the signature algorithms extension.

Why prioritize this

This vulnerability merits high-priority patching due to its CVSS 7.5 severity score, network accessibility, lack of authentication requirement, and potential for both denial of service and memory corruption. The straightforward exploitability and the ubiquity of WolfSSL in embedded and IoT environments increase real-world risk. Delayed patching leaves your infrastructure exposed to trivial remote attacks during TLS negotiation.

Risk score, explained

The CVSS 3.1 score of 7.5 (HIGH) reflects network attack vector, low complexity, no privilege requirement, and high integrity impact potential. Although confidentiality is not directly compromised, the out-of-bounds write can corrupt sensitive data structures or enable further exploitation. The absence of user interaction requirement and the global scope (no segmentation) further elevate the score. This is a straightforward remote code or crash vector that justifies urgent action.

Frequently asked questions