A flaw was reported  in how TBOOT handled measuring arguments to ELF kernels. When TBOOT is used on systems loading an ELF kernel, the first argument to any GRUB module may go unmeasured, which may result in undetected system compromise and violates the remote attestation that the argument measurement is intended to provide. This is fixed  in upstream version 1.8.2 and it is reported that all prior versions are vulnerable.
A CVE has been requested but not yet assigned .
Created tboot tracking bugs for this issue:
Affects: fedora-all [bug 1124489]
This was assigned CVE-2014-5118:
tboot-1.8.2-1.fc20 has been pushed to the Fedora 20 stable repository. If problems still persist, please make note of it in this bug report.
tboot-1.8.2-1.fc19 has been pushed to the Fedora 19 stable repository. If problems still persist, please make note of it in this bug report.
Alright, this is an interaction problem with GRUB2 (and possibly more, non-legacy-grub bootloaders). RHEL6 tboot may be vulnerable, but we don't ship GRUB2 with RHEL6, so I guess it's rather uncommon to see a vulnerable RHEL6 setup.
Upstream patch: http://sourceforge.net/p/tboot/code/ci/0efdaf7c5348701484d24562e6e5323d85bb94d3/
The tboot packages in Red Hat Enterprise Linux 7 were updated to upstream version 1.8.2 which includes the fix for this issue (see comment 6 above) via Red Hat Enterprise Linux 7.1 erratum RHBA-2015:0584:
The issue / fix is specific to use of tboot with grub 2. Red Hat Enterprise Linux 6 provides grub 0.97 and hence the issue is not planned to be addressed there.
Note that this issue may prevent detection of bootloader configuration change, which itself require attacker to have privileged local access.