Within the final 12 months and a half, attackers have exploited no less than 5 vulnerabilities — together with 4 zero-days — in a delicate, kernel-level Home windows driver.
A sequence of studies printed by Kaspersky’s Securelist this week lays out not only a handful of bugs, however a bigger, extra systemic concern within the present implementation of the Home windows Frequent Log File System (CLFS).
CLFS is a high-performance, general-purpose logging system out there for user- or kernel-mode software program purchasers. Its kernel entry makes it eminently helpful for hackers searching for low-level system privileges, and its performance-oriented design has left a sequence of safety holes in its wake lately, which ransomware actors particularly have pounced on.
“Kernel drivers must be very cautious when dealing with information, as a result of if a vulnerability is found, attackers can exploit it and acquire system privileges,” Boris Larin, principal safety researcher at Kaspersky’s World Analysis and Evaluation Group, tells Darkish Studying. Sadly, “design choices in Home windows CLFS have made it almost unimaginable to securely parse these CLFS information, which led to the emergence of an enormous variety of related vulnerabilities.”
The Drawback With Home windows CLFS
Win32k-level zero-days aren’t fully unusual, Larin conceded in his analysis. Nevertheless, he wrote, “we had by no means seen so many CLFS driver exploits being utilized in energetic assaults earlier than, after which instantly there are such a lot of of them captured in only one 12 months. Is there one thing significantly unsuitable with the CLFS driver?”
Nothing particularly modified concerning the CLFS driver this 12 months. Slightly, attackers appear to have simply now recognized what was unsuitable with it this entire time: It leans too far left in that inescapable, everlasting steadiness between efficiency and safety.
“CLFS is probably approach too ‘optimized for efficiency,'” Larin wrote, detailing the entire varied methods the driving force prioritizes it over safety. “It could be higher to have an affordable file format as a substitute of a dump of kernel buildings written to a file. All of the work with these kernel buildings (with pointers) occurs proper there within the blocks learn from disk. As a result of adjustments are made to the blocks and kernel buildings saved there, and people adjustments have to be flushed to disk, the code parses the blocks over and over each time it must entry one thing.”
He added, “All this parsing is completed utilizing relative offsets, which may level to any location inside a block. If one among these offsets turns into corrupted in reminiscence throughout execution, the implications will be catastrophic. However maybe worst of all, offsets within the BLF file on disk will be manipulated in such a approach that completely different buildings overlap, resulting in unexpected penalties.”
The sum of all of those design selections is efficient knowledge and occasion logging, but additionally loads of simply exploitable bugs. In 2023 alone there have been CVE-2022-24521, CVE-2022-37969, CVE-2023-23376, CVE-2023-28252 — all high-severity, 7.8-rated on the CVSS scale — used as zero-days, in addition to a fifth vulnerability that was patched earlier than any related malicious exercise was noticed within the wild. All of those had been leveraged by attackers, Kaspersky discovered — together with, for instance, the Nokoyawa ransomware group’s exploitation of CVE-2023-28252.
With out some form of redesign, CLFS could effectively proceed to supply escalation alternatives for hackers. To organize for that, Larin suggests, “organizations ought to deal with implementing the most effective safety practices: at all times set up safety updates on time, set up safety merchandise on all endpoints, prohibit entry to their servers and pay enormous consideration to anti-virus detections coming from the servers, prepare workers in order that they don’t change into victims of spear-phishing.”
