CVE-2026-46242 — Kernel
HIGHCVE-2026-46242 is a high-severity (CVSS 7.8) Use After Free vulnerability in Kernel. 1 public exploit reference exists, so weaponization risk is real. A fix is available for Kernel — see the affected versions and patch details below.
eventpoll: fix ep_remove struct eventpoll / struct file UAF
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-46242 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
KernelReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Linux packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐧Linux | Kernel | ≥ 5.16.0&&< 5.15.222 | 5.15.222 |
Affected Products
linux kernellinuxResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Kernel to 5.15.222 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-46242 is resolved across your whole dependency graph.
Workarounds
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
A race in eventpoll ep_remove() can let a concurrent file release observe a transient cleared file f_ep state and skip the normal eventpoll_release_file cleanup path. In the epoll watches epoll case this can free the watched struct eventpoll while ep_remove() still uses list pointers that refer into that freed object,…
Mitigation for this issue is either not available or the currently available options don't meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.Source: Red Hat security advisory for CVE-2026-46242 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| NVIDIA for RHEL 10 | kernel-0:6.12.0-231.15.el10nv | RHSA-2026:36186 |
| NVIDIA for RHEL 10 | kernel-0:6.12.0-259.26.el10nv | RHSA-2026:73187 |
| Red Hat Enterprise Linux 10 | kernel-0:6.12.0-211.31.1.el10_2 | RHSA-2026:36541 |
| Red Hat Enterprise Linux 10 | kpatch-patch | RHSA-2026:43826 |
| Red Hat Enterprise Linux 10.0 Extended Update Support | kernel-0:6.12.0-55.88.1.el10_0 | RHSA-2026:39371 |
| Red Hat Enterprise Linux 9 | kernel-0:5.14.0-687.23.1.el9_8 | RHSA-2026:36645 |
| Red Hat Enterprise Linux 9 | kpatch-patch | RHSA-2026:43825 |
| Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions | kernel-0:5.14.0-427.137.1.el9_4 | RHSA-2026:37729 |
Frequently Asked Questions
Is CVE-2026-46242 in your dependencies?
Find it across Linux, including transitive dependencies.