https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225668
Bug ID: 225668
Summary: 'su' command reads /etc/hosts and calls name
resolution erroneously
Product: Base System
Version: 11.1-RELEASE
Hardware: amd64
OS: Any
Status: New
Severity: Affects Many People
Priority: ---
Component: bin
Assignee: freebsd-bugs@FreeBSD.org
Reporter: f...@fehcom.de
Created attachment 190321
--> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=190321&action=edit
My /etc/hosts file + /etc/resolv.conf + capture of the name lookup following
the 'su' command
Hi,
upon calling 'su', su does the following:
- it reads /etc/hosts,
- it misinterprets an entry here with a colon as token in the first column,
- it uses a DNS stub resolver to forward this crippled name for unqualified
name resolution.
Given this behaviour, 'su' leaks information via DNS.
After forwarding the information to a DNS cache server, the initial call of
'su' waits for a time-out (about 500 msec). Usually, the cache server returns
NXDOMAIN following his cache, 'su' seems to work faster the following calls.
Attached you will find a documentation of this behaviour.
Regards.
--eh.
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