CVE-2026-46242

CVE Enrichment

CVSS: 7.8 HIGH
EPSS: 4.39%
EPSS Percentile: 91.28%
CISA KEV: Not listed

Description

In the Linux kernel, the following vulnerability has been resolved: eventpoll: fix ep_remove struct eventpoll / struct file UAF ep_remove() (via ep_remove_file()) cleared file->f_ep under file->f_lock but then kept using @file inside the critical section (is_file_epoll(), hlist_del_rcu() through the head, spin_unlock). A concurrent __fput() taking the eventpoll_release() fastpath in that window observed the transient NULL, skipped eventpoll_release_file() and ran to f_op->release / file_free(). For the epoll-watches-epoll case, f_op->release is ep_eventpoll_release() -> ep_clear_and_put() -> ep_free(), which kfree()s the watched struct eventpoll. Its embedded ->refs hlist_head is exactly where epi->fllink.pprev points, so the subsequent hlist_del_rcu()'s "*pprev = next" scribbles into freed kmalloc-192 memory. In addition, struct file is SLAB_TYPESAFE_BY_RCU, so the slot backing @file could be recycled by alloc_empty_file() -- reinitializing f_lock and f_ep -- while ep_remove() is still nominally inside that lock. The upshot is an attacker-controllable kmem_cache_free() against the wrong slab cache. Pin @file via epi_fget() at the top of ep_remove() and gate the critical section on the pin succeeding. With the pin held @file cannot reach refcount zero, which holds __fput() off and transitively keeps the watched struct eventpoll alive across the hlist_del_rcu() and the f_lock use, closing both UAFs. If the pin fails @file has already reached refcount zero and its __fput() is in flight. Because we bailed before clearing f_ep, that path takes the eventpoll_release() slow path into eventpoll_release_file() and blocks on ep->mtx until the waiter side's ep_clear_and_put() drops it. The bailed epi's share of ep->refcount stays intact, so the trailing ep_refcount_dec_and_test() in ep_clear_and_put() cannot free the eventpoll out from under eventpoll_release_file(); the orphaned epi is then cleaned up there. A successful pin also proves we are not racing eventpoll_release_file() on this epi, so drop the now-redundant re-check of epi->dying under f_lock. The cheap lockless READ_ONCE(epi->dying) fast-path bailout stays.

Technical Details

CVSS Version: 3.1
CNA / NVD Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Published: 30-May-2026 20:16
Last Modified: 20-Oct-2026 03:18
EPSS Date: 2026-10-28
CWE: CWE-416

CVSS Vector


            CVSS:3.1                            AV:L /
                            AC:L /
                            PR:L /
                            UI:N /
                            S:U /
                            C:H /
                            I:H /
                            A:H

Affected Products / Versions

linux / linux_kernel Source: NVD CPE · affected
Version / affected range: * · from (inclusive) 5.15.209 · before (exclusive) 5.16
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux / linux_kernel Source: NVD CPE · affected
Version / affected range: * · from (inclusive) 6.1.175 · before (exclusive) 6.2
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux / linux_kernel Source: NVD CPE · affected
Version / affected range: * · from (inclusive) 6.4 · before (exclusive) 6.18.33
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux / linux_kernel Source: NVD CPE · affected
Version / affected range: * · from (inclusive) 6.19 · before (exclusive) 7.0.10
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

References

Last enrichment sync: 29-Oct-2026 08:34
Sources: NVD · FIRST EPSS · CISA KEV
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Reported Context (3)

VEGA found GhostLock; days earlier, researchers disclosed Bad Epoll (CVE-2026-46242), a close cousin that also turns an unprivileged user into root. GhostLock Linux Kernel Flaw Enables Root Access and Container Escape
The security defect, tracked as CVE-2026-46242 (CVSS score of 7.8) and referred to as Bad Epoll, is described as a race-condition use-after-free bug in epoll, the Linux kernel’s I/O event notification facility. PoC Exploit Released for Linux Bad Epoll Root-Access Vulnerability
Bad Epoll (CVE-2026-46242) is a Linux kernel use-after-free flaw that can let a local user gain root on affected Linux desktops, servers, and Android devices, with a fix already available. Bad Epoll Linux Kernel Flaw Can Give Local Users Root on Linux and Android

CVE (5)

People (1)

MITRE ATT&CK (3)

Vendors (2)

Products (7)

Tools (2)

Note: Related entities, including threat actors, malware, CVEs, MITRE ATT&CK techniques, vendors, products, tools, countries, and industries, are shown when they appear in the same reporting. Their presence does not necessarily mean they were targeted, compromised, vulnerable, responsible for the activity, or directly involved in the incident.