CVE-2026-46242 — Linux Vulnerability Details

What is CVE-2026-46242?

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.

Its CVSS v3 base vector states that the flaw requires local access to the host, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 150 days ago.

Severity and exploitation probability

CVSS v3.1 base score: 7.8 — HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS (FIRST): 0.1% probability of exploitation in the next 30 days, higher than 6.5% of all scored CVEs
CISA KEV: Not listed in the CISA Known Exploited Vulnerabilities catalog
Threadlinqs priority: 6.2/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
Published: 2026-05-30, last modified 2026-10-03

Is CVE-2026-46242 being exploited?

Weaponised exploit code for CVE-2026-46242 is publicly available. 5 public proof-of-concept repositories are tracked for this identifier. It currently carries a trending score of 25 in the Threadlinqs vulnerability feed.

0xBlackash/CVE-2026-46242 (github)
Baba01hacker666/CVE-2026-46242 (github)
SaithFranklinB/ScannerBadEpoll (github)
villager1314/CVE-2026-46242-Analysis (github)
BinaryMasc/CVE-2026-46242 (github)

Affected products and versions

Linux: Linux

How to fix CVE-2026-46242

No vendor patch reference has been recorded for CVE-2026-46242 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

Threat activity tracking CVE-2026-46242

3 tracked threats in the Threadlinqs corpus reference CVE-2026-46242, either in the campaign’s CVE list or as an indicator on the campaign record.

CitrixBleed 2 (CVE-2025-5777) Exploited by Anubis Ransomware Affiliates Alongside Valid VPN Credentials and RMM Tool Abuse — CRITICAL · 2026-10-27
Bad Epoll (CVE-2026-46242): Use-After-Free Zero-Day in Linux Kernel epoll Subsystem Enables Root Privilege Escalation — HIGH · 2026-07-05
"Bad Epoll" Linux Kernel Use-After-Free (CVE-2026-46242) Enables Unprivileged Root Escalation, Impacts Android — HIGH · 2026-07-05

Sources

Enriched from CVE.org, FIRST EPSS, public proof-of-concept repositories. Last verified by Threadlinqs on 2026-10-10.

Other references

Showing 5 of 7 recorded references.