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[Bug libc/17625] wordexp fails to honour WRDE_NOCMD (CVE-2014-7817)
- From: "carlos at redhat dot com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Thu, 20 Nov 2014 15:56:11 +0000
- Subject: [Bug libc/17625] wordexp fails to honour WRDE_NOCMD (CVE-2014-7817)
- Auto-submitted: auto-generated
- References: <bug-17625-131 at http dot sourceware dot org/bugzilla/>
https://sourceware.org/bugzilla/show_bug.cgi?id=17625
--- Comment #3 from Carlos O'Donell <carlos at redhat dot com> ---
commit a39208bd7fb76c1b01c127b4c61f9bfd915bfe7c
Author: Carlos O'Donell <carlos@redhat.com>
Date: Wed Nov 19 11:44:12 2014 -0500
CVE-2014-7817: wordexp fails to honour WRDE_NOCMD.
The function wordexp() fails to properly handle the WRDE_NOCMD
flag when processing arithmetic inputs in the form of "$((... ``))"
where "..." can be anything valid. The backticks in the arithmetic
epxression are evaluated by in a shell even if WRDE_NOCMD forbade
command substitution. This allows an attacker to attempt to pass
dangerous commands via constructs of the above form, and bypass
the WRDE_NOCMD flag. This patch fixes this by checking for WRDE_NOCMD
in exec_comm(), the only place that can execute a shell. All other
checks for WRDE_NOCMD are superfluous and removed.
We expand the testsuite and add 3 new regression tests of roughly
the same form but with a couple of nested levels.
On top of the 3 new tests we add fork validation to the WRDE_NOCMD
testing. If any forks are detected during the execution of a wordexp()
call with WRDE_NOCMD, the test is marked as failed. This is slightly
heuristic since vfork might be used in the future, but it provides a
higher level of assurance that no shells were executed as part of
command substitution with WRDE_NOCMD in effect. In addition it doesn't
require libpthread or libdl, instead we use the public implementation
namespace function __register_atfork (already part of the public ABI
for libpthread).
Tested on x86_64 with no regressions.
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