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HomeCyber SecurityRansomware Attackers Abuse A number of Home windows CLFS Driver Zero-Days

Ransomware Attackers Abuse A number of Home windows CLFS Driver Zero-Days


Within the final 12 months and a half, attackers have exploited not less than 5 vulnerabilities — together with 4 zero-days — in a delicate, kernel-level Home windows driver.

A collection of studies revealed 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 shoppers. Its kernel entry makes it eminently helpful for hackers in search of low-level system privileges, and its performance-oriented design has left a collection of safety holes in its wake in recent times, which ransomware actors specifically 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 achieve system privileges,” Boris Larin, principal safety researcher at Kaspersky’s International Analysis and Evaluation Group, tells Darkish Studying. Sadly, “design selections in Home windows CLFS have made it practically not possible to securely parse these CLFS recordsdata, which led to the emergence of an enormous variety of comparable vulnerabilities.”

The Drawback With Home windows CLFS

Win32k-level zero-days aren’t totally 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 all of the sudden there are such a lot of of them captured in only one 12 months. Is there one thing significantly flawed with the CLFS driver?”

Nothing specifically modified concerning the CLFS driver this 12 months. Reasonably, attackers appear to have simply now recognized what was flawed with it this complete time: It leans too far left in that inescapable, everlasting stability between efficiency and safety.

“CLFS is probably means too ‘optimized for efficiency,'” Larin wrote, detailing all the 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 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 should be flushed to disk, the code parses the blocks time and again 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 one in every of these offsets turns into corrupted in reminiscence throughout execution, the results could be catastrophic. However maybe worst of all, offsets within the BLF file on disk could be manipulated in such a means that completely different constructions overlap, resulting in unexpected penalties.”

The sum of all of those design decisions 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 have 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 nicely proceed to supply escalation alternatives for hackers. To arrange for that, Larin suggests, “organizations ought to concentrate on implementing the very best safety practices: all the time set up safety updates on time, set up safety merchandise on all endpoints, limit entry to their servers and pay large consideration to anti-virus detections coming from the servers, practice staff in order that they don’t change into victims of spear-phishing.”



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