What is TLS Inspection?
TLS Inspection is the process of decrypting encrypted TLS traffic at a security control, examining the plaintext content, and re-encrypting it before forwarding it to its destination. It allows firewalls, proxies, and other security tools to detect threats hidden inside HTTPS and other TLS-protected connections.
What it is
TLS Inspection is a technique, not a product category. It is a capability built into security controls such as next-gen firewalls, secure web gateways, and Security Service Edge platforms.
When a client opens a TLS connection, the security device acts as a man-in-the-middle. It terminates the client's TLS session, decrypts the traffic, inspects the plaintext, then opens a new TLS session to the destination server. The client sees a certificate issued by the inspection device, not the origin server.
Why it matters
Roughly 90% of web traffic is encrypted. Attackers use TLS to hide malware downloads, command-and-control traffic, and data exfiltration. Without TLS Inspection, a firewall or IDS sees only encrypted bytes and cannot apply signature matching, sandboxing, or data loss prevention rules.
TLS Inspection lets security tools do their job on traffic that would otherwise pass through opaque.
How tools address it
Next-gen firewalls such as those in the Next-Gen Firewalls category perform TLS Inspection inline. The firewall holds a trusted CA certificate, issues a substitute certificate to the client, and decrypts traffic in the forwarding path. Some platforms extend this to cloud-delivered inspection through SASE or SSE architectures.
Key things to look for in any tool that performs TLS Inspection:
- Certificate trust management. The device's CA certificate must be distributed to all client trust stores, or users will see certificate errors.
- TLS version and cipher support. The tool must support TLS 1.3 and modern cipher suites, or it will fail to inspect newer connections.
- Policy-based bypass. Banking, healthcare, and other sensitive categories often need to be excluded from inspection for privacy or compliance reasons.