Proxy Connection and Certificate Issues

The most common ZAP issues involve proxy configuration and HTTPS certificate problems. When browsers cannot connect through ZAP's proxy, first verify ZAP is actually running and listening on the expected port. Check Tools > Options > Local Proxies to confirm the port (default 8080) and address settings. Ensure no other applications are using the same port by running netstat -an | grep 8080 on Linux/Mac or netstat -an | findstr 8080 on Windows.

Certificate errors preventing HTTPS site access frustrate many new users. ZAP generates a root certificate for HTTPS interception that browsers must trust. If you see certificate warnings, regenerate ZAP's root certificate through Tools > Options > Dynamic SSL Certificate. Save the certificate and import it into your browser's trusted certificate authorities. Each browser has different import procedures—Firefox maintains its own certificate store while Chrome uses the system store on most platforms.

Corporate proxy environments add complexity to ZAP configuration. If your organization requires proxy usage for internet access, configure ZAP to use the upstream proxy through Tools > Options > Connection. Enter your corporate proxy details including authentication if required. For applications requiring client certificates, import them through Options > Certificate. These layered proxy configurations often cause connection failures that systematic verification resolves.

# Diagnosing proxy issues on different platforms

# Linux/Mac - Check if ZAP is listening
lsof -i :8080
netstat -an | grep 8080

# Windows - Check port usage
netstat -an | findstr 8080
netstat -ab | findstr 8080

# Test proxy connectivity
curl -x http://localhost:8080 http://example.com

# Verify certificate installation
openssl s_client -connect example.com:443 -proxy localhost:8080