Bug 3500 - IPv6 address with embedded IP4v dot-decimal not honoured
Summary: IPv6 address with embedded IP4v dot-decimal not honoured
Status: NEW
Alias: None
Product: Portable OpenSSH
Classification: Unclassified
Component: ssh (show other bugs)
Version: 9.1p1
Hardware: Other Linux
: P5 enhancement
Assignee: Assigned to nobody
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2022-11-11 19:29 AEDT by martin ➬
Modified: 2022-11-11 19:29 AEDT (History)
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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.