|Summary:||wordexp fails to honour WRDE_NOCMD (CVE-2014-7817)|
|Product:||glibc||Reporter:||Carlos O'Donell <carlos>|
|Component:||libc||Assignee:||Not yet assigned to anyone <unassigned>|
Description Carlos O'Donell 2014-11-19 15:59:31 UTC
Placeholder bug for CVE-2014-7817.
Comment 1 Carlos O'Donell 2014-11-19 20:03:43 UTC
* CVE-2104-7817 The wordexp function could ignore the WRDE_NOCMD flag under certain input conditions resulting in the execution of a shell for command substitution when the applicaiton did not request it. The implementation now checks WRDE_NOCMD immediately before executing the shell and returns the error WRDE_CMDSUB as expected.
Comment 2 Carlos O'Donell 2014-11-19 20:04:13 UTC
Fixed on trunk.
Comment 3 Carlos O'Donell 2014-11-20 15:56:11 UTC
commit a39208bd7fb76c1b01c127b4c61f9bfd915bfe7c Author: Carlos O'Donell <firstname.lastname@example.org> 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.