{"description":"Trending threats, MITRE ATT\u0026CK coverage, and detection metadata. Fed continuously.","feed_url":"https://feed.craftedsignal.io/products/windows-common-log-file-system-driver/feed.json","home_page_url":"https://feed.craftedsignal.io/","items":[{"_cs_actors":[],"_cs_cpes":[],"_cs_cves":[{"cvss":7.8,"id":"CVE-2026-40407"}],"_cs_exploited":false,"_cs_has_poc":false,"_cs_poc_references":[],"_cs_products":["Windows Common Log File System Driver"],"_cs_severities":["high"],"_cs_tags":["privilege-escalation","heap-overflow","windows"],"_cs_type":"advisory","_cs_vendors":["Microsoft"],"content_html":"\u003cp\u003eCVE-2026-40407 is a heap-based buffer overflow vulnerability affecting the Windows Common Log File System (CLFS) Driver. This vulnerability allows an attacker with local access and valid credentials to escalate their privileges on a vulnerable system. The Common Log File System (CLFS) is a general-purpose logging service that can be used by software both in kernel-mode and user-mode to manage structured data records. A successful exploit of this vulnerability could allow an attacker to gain elevated system privileges, potentially leading to complete system compromise. Defenders should apply relevant patches as soon as possible.\u003c/p\u003e\n\u003ch2 id=\"attack-chain\"\u003eAttack Chain\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003eThe attacker gains initial access to the system with valid user credentials.\u003c/li\u003e\n\u003cli\u003eThe attacker crafts a malicious CLFS log file designed to trigger the heap overflow.\u003c/li\u003e\n\u003cli\u003eThe attacker interacts with the CLFS driver, causing it to parse the malicious log file.\u003c/li\u003e\n\u003cli\u003eThe CLFS driver allocates a heap buffer to store data from the log file.\u003c/li\u003e\n\u003cli\u003eDue to insufficient bounds checking, the driver writes beyond the allocated buffer, causing a heap overflow.\u003c/li\u003e\n\u003cli\u003eThe heap overflow corrupts adjacent heap metadata or data structures.\u003c/li\u003e\n\u003cli\u003eThe attacker leverages the heap corruption to overwrite critical system data or function pointers.\u003c/li\u003e\n\u003cli\u003eThe attacker triggers the overwritten function pointer, leading to arbitrary code execution with elevated privileges.\u003c/li\u003e\n\u003c/ol\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eSuccessful exploitation of CVE-2026-40407 allows a local attacker to elevate their privileges, potentially gaining SYSTEM level access. This could allow the attacker to perform a wide range of malicious activities, including installing programs, viewing, changing, or deleting data, or creating new accounts with full user rights. Given the widespread use of Windows, this vulnerability could potentially affect a large number of systems if exploited.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003eApply the security update released by Microsoft to patch CVE-2026-40407 (reference: \u003ca href=\"https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40407)\"\u003ehttps://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40407)\u003c/a\u003e.\u003c/li\u003e\n\u003cli\u003eEnable Sysmon process creation logging to monitor for unexpected processes spawned by CLFS-related binaries.\u003c/li\u003e\n\u003cli\u003eDeploy the Sigma rule provided below to detect potential exploitation attempts targeting CVE-2026-40407.\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2026-05-12T18:47:58Z","date_published":"2026-05-12T18:47:58Z","id":"https://feed.craftedsignal.io/briefs/2026-05-cve-2026-40407/","summary":"CVE-2026-40407 is a heap-based buffer overflow vulnerability in the Windows Common Log File System (CLFS) Driver, enabling a locally authenticated attacker to escalate privileges on the system.","title":"CVE-2026-40407 - Windows CLFS Driver Heap Overflow for Privilege Escalation","url":"https://feed.craftedsignal.io/briefs/2026-05-cve-2026-40407/"},{"_cs_actors":[],"_cs_cpes":[],"_cs_cves":[{"cvss":7.8,"id":"CVE-2026-40397"}],"_cs_exploited":false,"_cs_has_poc":false,"_cs_poc_references":[],"_cs_products":["Windows Common Log File System Driver"],"_cs_severities":["high"],"_cs_tags":["privilege-escalation","windows"],"_cs_type":"advisory","_cs_vendors":["Microsoft"],"content_html":"\u003cp\u003eCVE-2026-40397 is an integer underflow vulnerability affecting the Windows Common Log File System (CLFS) driver. This vulnerability allows a locally authenticated attacker to escalate their privileges. The vulnerability resides within the CLFS driver\u0026rsquo;s handling of specific data structures, where an integer underflow can occur during size calculations or memory allocation. Successful exploitation allows an attacker to execute arbitrary code with elevated privileges, potentially gaining complete control over the affected system. The vulnerability was publicly disclosed on May 12, 2026, and is documented in Microsoft\u0026rsquo;s security update guide.\u003c/p\u003e\n\u003ch2 id=\"attack-chain\"\u003eAttack Chain\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003eAn attacker gains local access to a Windows system.\u003c/li\u003e\n\u003cli\u003eThe attacker crafts a specially crafted input to the CLFS driver.\u003c/li\u003e\n\u003cli\u003eThe crafted input triggers an integer underflow within the CLFS driver during a size calculation.\u003c/li\u003e\n\u003cli\u003eThe integer underflow leads to an undersized buffer allocation.\u003c/li\u003e\n\u003cli\u003eThe attacker triggers a write operation to the undersized buffer.\u003c/li\u003e\n\u003cli\u003eThe write operation overflows the buffer, corrupting adjacent memory.\u003c/li\u003e\n\u003cli\u003eThe corrupted memory contains critical system data or function pointers.\u003c/li\u003e\n\u003cli\u003eThe attacker leverages the memory corruption to execute arbitrary code with elevated privileges.\u003c/li\u003e\n\u003c/ol\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eSuccessful exploitation of CVE-2026-40397 leads to local privilege escalation on the affected Windows system. An attacker can leverage this vulnerability to gain SYSTEM privileges, allowing them to install programs, view, change, or delete data, or create new accounts with full user rights. While the specific number of affected systems is not detailed, this vulnerability affects any Windows system where the CLFS driver is enabled, posing a significant risk to organizations if left unpatched.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003eApply the security updates released by Microsoft to patch CVE-2026-40397 on all affected Windows systems.\u003c/li\u003e\n\u003cli\u003eMonitor for suspicious activity related to CLFS driver usage, such as unusual memory allocations or write operations using the \u0026ldquo;Detect CLFS Integer Underflow Exploitation via Process Creation\u0026rdquo; Sigma rule.\u003c/li\u003e\n\u003cli\u003eEnable process creation logging to capture relevant events for the detection rule above.\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2026-05-12T18:46:07Z","date_published":"2026-05-12T18:46:07Z","id":"https://feed.craftedsignal.io/briefs/2026-05-cve-2026-40397/","summary":"CVE-2026-40397 is an integer underflow vulnerability in the Windows Common Log File System (CLFS) driver that allows an authenticated attacker to escalate privileges locally.","title":"CVE-2026-40397: Windows CLFS Driver Integer Underflow Privilege Escalation","url":"https://feed.craftedsignal.io/briefs/2026-05-cve-2026-40397/"}],"language":"en","title":"CraftedSignal Threat Feed — Windows Common Log File System Driver","version":"https://jsonfeed.org/version/1.1"}