A Trio of Vulnerabilities in the Linux Kernel Can Give Attackers Root Privileges

Linux kernel distributions appear explicitly susceptible to recently uncovered vulnerabilities. In the iSCSI module, which is used for viewing shared data storages, three unearthed vulnerabilities in the Linux kernel would provide administrative privileges to anybody with a user account. Since 2006, the Linux code has no identification of the trio of defects – the CVE-2021-27363, CVE-2021-27364, and CVE-2021-27365 – until GRIMM researchers found them. 

“If you already had the execution on a box, either because you have a user account on the machine, or you’ve compromised some service that doesn’t have repaired permissions, you can do whatever you want basically,” said Adam Nichols, principal of the Software Security practice at GRIMM. 

Although the vulnerabilities that are in code, are not functional remotely, therefore they are not remote exploits but are still troubling. They take “any existing threat that might be there. It just makes it that much worse,” he explained. Referring to the concept that “many eyes make any bug shallow,” Linux code doesn’t get many eyes so that it seems perfect. But while the code was first published, the bugs have been there, even in the last fifteen years they haven’t really modified. 

GRIMM researchers, of course, are trying to dig in to see how often vulnerabilities occur where possible – with open source, a much more feasible solution. It’s very much related to the extent of the Linux kernel that the defections drifted away. “It gotten so big,” Nichols said, “there’s so much code there.” “The real strategy is making sure you’re loading as little code as possible.” 

Nichols said that bugs are present in all Linux distributions, but kernel drivers are not enabled by default. If the vulnerable kernel module can be loaded by a regular user or not, may vary. For example, they could be checked by GRIMM in all Red Hat distros. “Even though it’s not loaded by default, you can load it and you can exploit it without any trouble,” added Nichols. 

Although the hardware is present, other systems such as Debian and Ubuntu “are in the same boat as Red Hat, where the user, depending on what packages are installed, can coerce it into getting loaded; then it’s there to be exploited,” he said. Errors are reported in 5.11.4, 5.10.21, 5.4.103, 4.19.179, 4.14.224, 4.9.260, and 4.4.260. The bugs are not included in the following updates. Although all the old kernels are end-of-life and will not be patched. 

Nichols suggests that the Kernel must be blacklisted as a temporary measure to neutralize defects. “Any system that doesn’t use that module can just say never load this module under any circumstances, and then you’re kept safe,” he said. But “if you’re actually using iSCSI, then you wouldn’t want to do that.”