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Date: Fri, 16 Sep 2016 17:16:06 +0100
From: John Haxby <john.haxby@...cle.com>
To: oss-security@...ts.openwall.com
Cc: chet.ramey@...e.edu
Subject: CVE-2016-0634 -- bash prompt expanding $HOSTNAME
Hello All,
A little while ago, one of our users discovered that by setting the
hostname to $(something unpleasant), bash would run "something
unpleasant" when it expanded \h in the prompt string.
We informed Chet (cc'd) and this has been fixed in the recently
announced bash-4.4.
I believe the fix in parse.y is this (Chet, please correct me if I'm wrong):
--------------------
@@ -5569,9 +5703,17 @@ decode_prompt_string (string)
case 'h':
case 'H':
- temp = savestring (current_host_name);
- if (c == 'h' && (t = (char *)strchr (temp, '.')))
+ t_host = savestring (current_host_name);
+ if (c == 'h' && (t = (char *)strchr (t_host, '.')))
*t = '\0';
+ if (promptvars || posixly_correct)
+ /* Make sure that expand_prompt_string is called with a
+ second argument of Q_DOUBLE_QUOTES if we use this
+ function here. */
+ temp = sh_backslash_quote_for_double_quotes (t_host);
+ else
+ temp = savestring (t_host);
+ free (t_host);
goto add_string;
case '#':
--------------------
There is a related fix (but not one necessarily covered by CVE-2016-0634):
--------------------
@@ -5479,7 +5609,11 @@ decode_prompt_string (string)
case 's':
temp = base_pathname (shell_name);
- temp = savestring (temp);
+ /* Try to quote anything the user can set in the file system */
+ if (promptvars || posixly_correct)
+ temp = sh_backslash_quote_for_double_quotes (temp);
+ else
+ temp = savestring (temp);
goto add_string;
case 'v':
--------------------
I appreciate that it's relatively difficult to set the hostname to a
string of your choosing but there are plenty of helpful agents that will
call sethostname(2) on your behalf.
jch
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