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 collection of reviews 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 Widespread 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 looking for 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 information, 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 Staff, tells Darkish Studying. Sadly, “design selections in Home windows CLFS have made it almost not possible to securely parse these CLFS information, which led to the emergence of an enormous variety of comparable vulnerabilities.”
The Downside With Home windows CLFS
Win32k-level zero-days aren’t completely unusual, Larin conceded in his analysis. Nevertheless, he wrote, “we had by no means seen so many CLFS driver exploits being utilized in lively assaults earlier than, after which out of the blue there are such a lot of of them captured in only one 12 months. Is there one thing severely unsuitable with the CLFS driver?”
Nothing specifically modified concerning the CLFS driver this 12 months. Relatively, attackers appear to have simply now recognized what was unsuitable with it this complete time: It leans too far left in that inescapable, everlasting stability between efficiency and safety.
“CLFS is maybe means too ‘optimized for efficiency,'” Larin wrote, detailing the entire varied methods the motive force prioritizes it over safety. “It could be higher to have an inexpensive 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 must be flushed to disk, the code parses the blocks again 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 certainly one of these offsets turns into corrupted in reminiscence throughout execution, the implications may be catastrophic. However maybe worst of all, offsets within the BLF file on disk may be manipulated in such a means 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 have been leveraged by attackers, Kaspersky discovered — together with, for instance, the Nokoyawa ransomware group’s exploitation of CVE-2023-28252.
With out some type of redesign, CLFS could effectively proceed to supply escalation alternatives for hackers. To organize for that, Larin suggests, “organizations ought to give attention to implementing the very best 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 large consideration to anti-virus detections coming from the servers, practice staff in order that they don’t turn into victims of spear-phishing.”
