Within the final 12 months and a half, attackers have exploited at the least 5 vulnerabilities — together with 4 zero-days — in a delicate, kernel-level Home windows driver.

A sequence of experiences revealed by Kaspersky’s Securelist this week lays out not only a handful of bugs, however a bigger, extra systemic subject within the present implementation of the Home windows Widespread Log File System (CLFS).

CLFS is a high-performance, general-purpose logging system obtainable for user- or kernel-mode software program purchasers. Its kernel entry makes it eminently helpful for hackers looking for low-level system privileges, and its performance-oriented design has left a sequence of safety holes in its wake in recent times, which ransomware actors particularly have pounced on.

“Kernel drivers must be very cautious when dealing with recordsdata, 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 International Analysis and Evaluation Staff, tells Darkish Studying. Sadly, “design selections in Home windows CLFS have made it practically inconceivable to securely parse these CLFS recordsdata, which led to the emergence of an enormous variety of related vulnerabilities.”

The Drawback With Home windows CLFS

Win32k-level zero-days aren’t completely unusual, Larin conceded in his analysis. Nonetheless, he wrote, “we had by no means seen so many CLFS driver exploits being utilized in energetic assaults earlier than, after which all of the sudden there are such a lot of of them captured in only one 12 months. Is there one thing significantly mistaken with the CLFS driver?”

Nothing particularly modified concerning the CLFS driver this 12 months. Relatively, attackers appear to have simply now recognized what was mistaken with it this complete time: It leans too far left in that inescapable, everlasting stability 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 inexpensive file format as a substitute of a dump of kernel constructions written to a file. All of the work with these kernel constructions (with pointers) occurs proper there within the blocks learn from disk. As a result of adjustments are made to the blocks and kernel constructions saved there, and people adjustments must 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 finished utilizing relative offsets, which might level to any location inside a block. If considered one of 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 constructions overlap, resulting in unexpected penalties.”

The sum of all of those design decisions is efficient information and occasion logging, but in addition 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 kind of redesign, CLFS could properly proceed to supply escalation alternatives for hackers. To organize for that, Larin suggests, “organizations ought to concentrate on implementing one of the best safety practices: at all times set up safety updates on time, set up safety merchandise on all endpoints, limit entry to their servers and pay enormous consideration to anti-virus detections coming from the servers, prepare workers in order that they don’t turn out to be victims of spear-phishing.”