Date: Mon, 13 Oct 2014 14:49:51 +0200 From: Sebastian Krahmer <krahmer@...e.de> To: oss-security@...ts.openwall.com Subject: shim RCE Hi As per policy-request, here is the oss-posting of what has formerly been negotiated on distros@. Initial CRD was Oct 6th but has been shellshokshifted to today upon request. -- We reviewed some parts of the shim trusted bootloader. Shim is responsible for verifying of - and chaining into - a next level bootloader. Shim itself is signed by MS so it can be loaded by UEFI secure boot aware boards. These vulnerabilities could be exploited to bypass "secure boot" with leverage up to OS level. We found three issues that should be fixed: 1. OOB read access when parsing DHCPv6 packets (remote DoS). The severity is low. (CVE-2014-3675) 2. Heap overflow when parsing IPv6 addresses provided by tftp:// DHCPv6 boot option (RCE). The severity is low to medium, as secure boot via PXE6 should rarely be seen ITW. Furthermore UEFI firmware seems to fail to properly verify provided PXE images at the first place. (CVE-2014-3676) For both issues above there is a patch proposal: http://suse.com/~krahmer/priv/shim1.diff 3. Memory corruption when processing user provided MOK lists. Its unclear whether this could lead to a code execution in the secure boot path. (CVE-2014-3677) For this issue there is also a patch proposal: http://suse.com/~krahmer/priv/shim2.diff All three issues should receive a CVE each. We ask for a CRD of Oct 6th. 2014. When updating, vendors should also take care to include git commit 45ab8962ae7c8e860a45d195cfe8a3f4d8aec4c7 since this already fixes another overflow (different from 2.) when parsing DHCPv6 packets. We did _not_ conduct a full code review of shim. In particular PE header parsing and relocating of PE EFI images is left untouched. Upstream maintainers have been informed already, as well as MS to initiate the signing process of a patched shim. It's unfortunate for Open Source vendors to rely on a third party being a milestone in an update process since its adds hereto a lot of complexity in the coordination and updating process. Sebastian -- ~ perl self.pl ~ $_='print"\$_=\47$_\47;eval"';eval ~ krahmer@...e.de - SuSE Security Team
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