Bug 3500

Summary: IPv6 address with embedded IP4v dot-decimal not honoured
Product: Portable OpenSSH Reporter: martin ➬ <bugzilla.mindrot.org>
Component: sshAssignee: Assigned to nobody <unassigned-bugs>
Status: NEW ---    
Severity: enhancement    
Priority: P5    
Version: 9.1p1   
Hardware: Other   
OS: Linux   

Description martin ➬ 2022-11-11 19:29:41 AEDT 
A valid IPv6 address can end with a IPv4 dot-decimal, such as:

2001:db8:4321::192.0.2.123

which effectively translates to

2001:db8:4321::c000:027b

i.e. the 32 bits of the IPv4 address are simply mapped to the last two fields of the IPv6 address.

When an SSH known_hosts file contains a line like:

example.org,192.0.2.123,2001:db8:4321::192.0.2.123 ssh-ed25519 …

then on a v6 connection, a new line is added to the known_hosts file, which is just the translated IPv6 address, e.g.

2001:db8:4321::c000:027b ssh-ed25519 …

This creates redundant information, and it would be better if SSH recognised that the IPv6 address is already used and mapped to a host fingerprint.