Gabriel VLASIU reported [1] that yum-cron would install unsigned RPM packages that yum itself would refuse to install. The yum-cron code is based on that in yum-updatesd.py. This is due to the installUpdates() function (processPkgs() in yum-updatesd.py) failing to fully check the return code of the called sigCheckPkg() function. sigCheckPkg() is described thus:

def sigCheckPkg(self, po): """Verify the GPG signature of the given package object.

:param po: the package object to verify the signature of :return: (result, errorstring) where result is::

0 = GPG signature verifies ok or verification is not required. 1 = GPG verification failed but installation of the right GPG key might help. 2 = Fatal GPG verification error, give up. """

However, the processPkgs() and installUpdates() calling function do not account for return code 2:

def processPkgs(self, dlpkgs): ... for po in dlpkgs: result, err = self.updd.sigCheckPkg(po) if result == 0: continue elif result == 1: try: self.updd.getKeyForPackage(po) except yum.Errors.YumBaseError, errmsg: self.failed([str(errmsg)])

and:

def installUpdates(self, emit): ... for po in dlpkgs: result, err = self.sigCheckPkg(po) if result == 0: continue elif result == 1: try: self.getKeyForPackage(po) except yum.Errors.YumBaseError, errmsg: self.emitUpdateFailed(errmsg) return False

yum-cron.py replaced yum-cron.sh in Fedora 19 (3.4.3-47); earlier versions of Fedora use yum-updatesd.

This has been corrected upstream [2] and in Fedora via yum-3.4.3-132.fc19 and yum-3.4.3-130.fc20.

This does not affect Red Hat Enterprise Linux 6 as it used neither yum-updatesd nor yum-cron; it used a shellscript that called yum itself to do updates.

[1] https://bugzilla.redhat.com/showbug.cgi?id=1052440 [2] http://yum.baseurl.org/gitweb?p=yum.git;a=commitdiff;h=9df69e579496ccb6df5c3f5b5b7bab8d648b06b4

yum does not properly handle bad metadata, which allows an attacker to cause a denial of service and possibly have other unspecified impact via a Trojan horse file in the metadata of a remote repository.