Within the final yr 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 reviews printed by Kaspersky’s Securelist this week lays out not only a handful of bugs, however a bigger, extra systemic difficulty within the present implementation of the Home windows Frequent 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 specifically have pounced on.
“Kernel drivers ought to 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 World Analysis and Evaluation Workforce, tells Darkish Studying. Sadly, “design selections in Home windows CLFS have made it practically inconceivable 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 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 abruptly there are such a lot of of them captured in only one yr. Is there one thing severely mistaken with the CLFS driver?”
Nothing specifically modified in regards to the CLFS driver this yr. Quite, attackers appear to have simply now recognized what was mistaken with it this entire time: It leans too far left in that inescapable, everlasting stability between efficiency and safety.
“CLFS is probably method too ‘optimized for efficiency,'” Larin wrote, detailing the entire numerous methods the driving force prioritizes it over safety. “It might 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 modifications are made to the blocks and kernel buildings saved there, and people modifications should 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 may level to any location inside a block. If certainly one of these offsets turns into corrupted in reminiscence throughout execution, the results may be catastrophic. However maybe worst of all, offsets within the BLF file on disk may be manipulated in such a method that completely different buildings overlap, resulting in unexpected penalties.”
The sum of all of those design selections is efficient knowledge 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 form of redesign, CLFS could nicely proceed to supply escalation alternatives for hackers. To arrange for that, Larin suggests, “organizations ought to deal with implementing one of the 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, prepare staff in order that they don’t develop into victims of spear-phishing.”
