pedit COW (CVE-2026-46331): Mitigation and Kernel Update on CloudLinux

On June 17, 2026, researcher Massimiliano Oldani published a working proof-of-concept named packet_edit_meme for a Linux kernel local privilege escalation now tracked as CVE-2026-46331 and nicknamed pedit COW. The flaw is in the kernel’s traffic-control (tc) subsystem. Any unprivileged local user on an affected host can use it to gain root in a single command.

The vulnerable code is the act_pedit traffic-control action, which edits packet headers in place. It computes its copy-on-write (COW) range once, before editing, but misses the runtime offset that typed keys add at execution time, so it ends up writing into a page it never made private. This partial COW lets the write reach shared page-cache memory backing a real file, which the kernel believed it had made safe to modify. By controlling the offset, an unprivileged process turns this into a write into the page-cache copy of a file it could otherwise only read. The CAP_NET_ADMIN capability needed to configure the action does not require real privilege: it is obtained inside an unprivileged user + network namespace, which is available to ordinary users by default on the EL family.

The published PoC targets setuid-root /bin/su directly: it overwrites the cached ELF entry point of the binary with shellcode equivalent to setgid(0); setuid(0); execve(“/bin/sh”), so the next su invocation runs as root.

Details: public PoC · upstream fix · Red Hat CVE entry · Ubuntu CVE entry · TuxCare analysis

Affected CloudLinux versions

Version	Affected	Will be patched via
CloudLinux 7 (CL7)	✅ No	—
CloudLinux 7h (CL7h)	❌ Yes	CloudLinux kernel
CloudLinux 8 (CL8)	❌ Yes	CloudLinux kernel
CloudLinux 9 (CL9)	❌ Yes	AlmaLinux kernel
CloudLinux 10 (CL10)	❌ Yes	AlmaLinux kernel
CloudLinux for Ubuntu 22.04 LTS	❌ Yes	Ubuntu kernel update + KernelCare livepatch

A KernelCare livepatch that deploys the fix without a reboot will also be available as an alternative on all affected versions. See Stream 3 below for current status.

Apply this mitigation now

Until a patched kernel or KernelCare livepatch is installed, apply one of the two mitigations below. Either one closes the attack; choose the one that fits your workload.

Option A — Block the act_pedit module

If you do not use traffic-control pedit rules (the typical web-hosting server does not), prevent the module from loading and unload it if it is already present:

echo 'install act_pedit /bin/true' | sudo tee /etc/modprobe.d/disable-act_pedit.conf
lsmod | grep -w act_pedit && sudo rmmod act_pedit

To revert after a patched kernel is installed:

sudo rm /etc/modprobe.d/disable-act_pedit.conf

Compatibility: with this rule in place, any traffic-control configuration that uses the pedit action will fail to load. Do not apply it on hosts that rely on tc … action pedit rules.

Option B — Restrict unprivileged user namespaces

This removes the CAP_NET_ADMIN acquisition path the exploit relies on, without touching the tc subsystem.

On the EL family (CL7h, CL8, CL9, CL10):

sudo sysctl -w user.max_user_namespaces=0
echo 'user.max_user_namespaces = 0' | sudo tee /etc/sysctl.d/99-pedit-cow.conf

On CloudLinux for Ubuntu 22.04:

sudo sysctl -w kernel.unprivileged_userns_clone=0
echo 'kernel.unprivileged_userns_clone = 0' | sudo tee /etc/sysctl.d/99-pedit-cow.conf

Compatibility: unprivileged user namespaces are required by rootless container runtimes and several CI sandboxes. Restricting them is acceptable on hardened or hosting workloads, but disruptive on developer and container hosts. Do not apply this option where those workloads run.

Restore page-cache binaries after mitigation

The exploit modifies a legitimate system binary (the public PoC overwrites /bin/su) in the page cache as part of gaining root, so applying a mitigation alone is not enough on systems that may have been targeted before the mitigation was in place. After mitigating, drop the page cache to force a reload from disk:

sudo sh -c "echo 3 > /proc/sys/vm/drop_caches"

This is containment, not remediation. Dropping the cache evicts a poisoned copy, but if an attacker already reached root, eviction does not remove persistence they established afterward. If you suspect a host was compromised, treat it as compromised and rebuild.

Update instructions

There are three release streams, plus a separate path for CloudLinux for Ubuntu 22.04. Use the one that applies to your CloudLinux version. As patches land, this article will be updated in place. Check the timestamps on the callouts in each stream below.

Stream 1 — CloudLinux kernel (CL7h, CL8)

Both are CloudLinux rebuilds of the upstream fix.

Updating from the CloudLinux beta channel

Because the stable rollout is gradual, use the beta channel if you want to install immediately.

Instructions for updating CL8 from the beta channel — cloudlinux-updates-testing:

yum --enablerepo=cloudlinux-updates-testing update 'kernel*'
reboot
uname -r

Instructions for updating CL7h from the beta channel — cl7h_beta:

yum --enablerepo=cl7h_beta update 'kernel*'
reboot
uname -r

Updating from the CloudLinux stable channel

Once the kernel reaches the stable channel for your server, a plain update will pull the patched version, no extra repo enablement needed:

yum update 'kernel*'
reboot
uname -r

 

Stream 2 — AlmaLinux kernel (CL9, CL10)

CloudLinux 9 and CloudLinux 10 use the AlmaLinux kernel directly. The patched kernel is already in the production repositories, so a plain update pulls it:

dnf update 'kernel*'
reboot
uname -r

 

Stream 3 — KernelCare livepatch (all affected versions)

The KernelCare livepatch for this vulnerability is being prepared. KernelCare ships it to the testing feed first and promotes to the main feed after validation. To deploy from the testing feed once available:

kcarectl --update --prefix test

Once promoted to the main feed, KernelCare-subscribed systems receive the fix automatically through the standard livepatch flow:

kcarectl --update

Not using KernelCare yet? You can roll the fix out across your entire fleet automatically, without reboots. Get started in a few minutes — more information here.

 

CloudLinux for Ubuntu 22.04 LTS

CloudLinux for Ubuntu 22.04 runs the stock Ubuntu kernel; there is no CloudLinux-built kernel for this platform, and the production fix arrives from Canonical via apt. Track its status on the Ubuntu CVE page.

 

How to verify you are patched

After update + reboot:

uname -r

Compare to the target version for your CloudLinux stream above.

For KernelCare:

kcarectl --info | grep kpatch-build-time

A build time on or after the livepatch publish date includes the pedit COW fix. Alternatively, once patch metadata is finalized:

kcarectl --patch-info | grep CVE-2026-46331

 

References