What
In auto mode, the Bash tool can take an allowed_domains list for a single command, naming the hosts that command may reach over the network. Claude Code already rejected entries that write a loopback address (your own machine) or an IPv4 host in a disguised form, such as an IPv4-mapped or NAT64 IPv6 address. That check now also looks inside a leading pair of square brackets. Bracketed forms, including ones with a port number, can no longer get past it. The error still tells you to allow the plain dotted IPv4 address or the real host name instead.
Why
In auto mode Claude supplies the host list itself, so this closes a way around the sandbox's network check. The sandbox is the walled-off environment that commands run in.
Names in the bundleallowed_domains
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
Exactly which bracketed addresses got past the check before is not settled.