Within the final yr 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 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 shoppers. 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 ought to 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 Group, tells Darkish Studying. Sadly, “design choices in Home windows CLFS have made it practically unattainable to securely parse these CLFS recordsdata, which led to the emergence of an enormous variety of related vulnerabilities.”
The Downside 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 lively assaults earlier than, after which all of the sudden there are such a lot of of them captured in only one yr. Is there one thing critically improper with the CLFS driver?”
Nothing particularly modified concerning the CLFS driver this yr. Fairly, attackers appear to have simply now recognized what was improper with it this complete 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 all the varied methods the driving force prioritizes it over safety. “It might be higher to have an affordable file format as an alternative 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 modifications are made to the blocks and kernel constructions saved there, and people modifications 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 may level to any location inside a block. If considered one of these offsets turns into corrupted in reminiscence throughout execution, the results might be catastrophic. However maybe worst of all, offsets within the BLF file on disk might be manipulated in such a approach that totally different constructions overlap, resulting in unexpected penalties.”
The sum of all of those design decisions 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 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 might 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: all the time 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.”
