Ensuring that IPv4 is allowed

Sometimes, Java picks up the IPv6 address on the interface, and Burp is unable to make any connections to websites returning an IPv4 address. This results in a Java error, which is as follows:

java.net.SocketException: Permission denied

The browser also shows a cryptic error, which is as follows:

Burp proxy error: Permission denied: connect

If we ever encounter this error, all we need to do is tell Java that we want to use the IPv4 interface by passing the following parameter to the runtime:

java -Xmx2048M -Djava.net.preferIPv4Stack=true -jar /path/to/burpsuite.jar

This command and flag tells the Java runtime that we will prefer the IPv4 network stack to run the Burp Suite JAR file. Another option is to set a Java option environment variable.

Please note that by running the preceding command, the IPv6 interface will be disabled.

Many people have reported this as a bug on the Burp support forums. Most of the people who complained were using Microsoft Windows 7 64-bit operating system running a 32-bit version of the JVM.