CloudLinux has warned about a new Linux kernel vulnerability, identified as CVE-2026-31431 and known as “Copy Fail”, affecting CloudLinux 7h, 8, 9, and 10. The company warns that an unprivileged local user can escalate privileges to root if the system is vulnerable and no mitigation or patched kernel has been applied.
The advisory is especially relevant for hosting providers, shared server administrators, multi-user environments, and platforms where customer accounts coexist on the same system. CloudLinux 7 is not affected, but CloudLinux 7h, CloudLinux 8, CloudLinux 9, and CloudLinux 10 are within the risk scope. The company is preparing patched kernels and KernelCare livepatches, but recommends applying a temporary mitigation while the final updates become available.
What CVE-2026-31431 is and why it matters
Copy Fail is a local privilege escalation vulnerability in the algif_aead component, related to the Linux kernel’s AF_ALG cryptographic interface. In simple terms, the flaw may allow an already authenticated user on the system to manipulate kernel memory in a way that ultimately grants administrator privileges.
It is not a remote vulnerability that allows attackers to break in directly from the internet without credentials, but that does not make it minor. On multi-user servers, hosting panels, environments with SSH accounts, containers, scheduled tasks, or compromised applications, an attacker who has already obtained limited access could use a local vulnerability to take full control of the system.
The case is also concerning because the issue affects Linux kernels released over several years and because enough technical information is already public for administrators to treat it as a priority. CERT-EU has rated the vulnerability as high severity, with a CVSS score of 7.8, and the NVD database tracks the flaw in the kernel’s cryptographic subsystem.
In CloudLinux, the impact varies by version. CloudLinux 7 is not affected. CloudLinux 7h and CloudLinux 8 will receive patched CloudLinux kernels. CloudLinux 9 and 10 rely directly on the AlmaLinux kernel, so the fix will arrive through that channel. KernelCare will provide livepatching for affected versions, allowing systems with a subscription to be fixed without a reboot once the corresponding update is released.
| Version | Status | Expected fix path |
|---|---|---|
| CloudLinux 7 | Not affected | No patch required for this CVE |
| CloudLinux 7h | Affected | CloudLinux kernel and KernelCare |
| CloudLinux 8 | Affected | CloudLinux kernel and KernelCare |
| CloudLinux 9 | Affected | AlmaLinux kernel and KernelCare |
| CloudLinux 10 | Affected | AlmaLinux kernel and KernelCare |
The mitigation recommended by CloudLinux
Until final kernels or the KernelCare livepatch are available, CloudLinux recommends blocking the initialization of algif_aead using a kernel parameter managed with grubby. The mitigation requires a server reboot, but it can be reverted quickly once the patch has been installed.
The command recommended by CloudLinux is:
sudo grubby --update-kernel=ALL --args="initcall_blacklist=algif_aead_init"
sudo rebootCode language: JavaScript (javascript)After rebooting, administrators should verify that the parameter has been applied:
sudo grubby --info=ALL | grep initcall_blacklistOnce the system is running a patched kernel, the mitigation can be removed with:
sudo grubby --update-kernel=ALL --remove-args="initcall_blacklist=algif_aead_init"
sudo rebootCode language: JavaScript (javascript)CloudLinux highlights an important point: a mitigation circulating on security mailing lists based on modprobe.d does not work on CloudLinux, AlmaLinux, or other RHEL-family distributions when algif_aead is built into the kernel. In those cases, adding a rule such as install algif_aead /bin/false may create a false sense of protection, because the component is not loaded as an external module and cannot be blocked that way.
This detail matters for administrators managing many servers. Applying a generic workaround copied from another distribution may provide no protection at all. For CloudLinux, the current recommendation is to use the grubby method until the kernel or livepatch is available.
What administrators should prioritize
The first priority is to identify CloudLinux 7h, 8, 9, and 10 systems with local users or multi-user workloads. Shared hosting, servers with customer SSH access, containerized environments, or machines where several applications run under separate permissions face a higher operational risk.
The second priority is to choose between temporary mitigation and a patching window. If KernelCare is deployed, administrators should monitor the livepatch status and run the usual update flow once it is available. Without livepatching, the patched kernel installation and reboot must be planned. In the meantime, CloudLinux recommends applying the grubby mitigation.
The third step is to review actual exposure. Although this is a local privilege escalation, many intrusions start with a limited account, a compromised web application, or a low-privileged user. A local root vulnerability can turn that initial foothold into full server compromise.
Telemetry and logs should also be reviewed. CloudLinux says Imunify360 already detects published indicators of compromise and uses extended heuristics to identify emerging signals. Even so, the company stresses that Imunify360 is an additional layer of defense, not a replacement for the kernel patch.
| Recommended action | Purpose |
|---|---|
| Identify affected CloudLinux versions | Prioritize 7h, 8, 9, and 10 systems |
Apply the grubby mitigation | Reduce attack surface until patching |
Avoid the modprobe.d workaround | Do not rely on a mitigation that does not apply to RHEL-family kernels |
| Monitor KernelCare and CloudLinux Status | Install the livepatch or patched kernel as soon as available |
| Review local access and logs | Detect possible exploitation attempts |
| Remove the mitigation after patching | Keep the system clean once fixed |
A serious warning for hosting providers
Copy Fail is a reminder that the kernel remains a critical component in any hosting service. Isolation layers, users, cages, containers, and security policies reduce risk, but a local privilege escalation can break much of that separation if it is not fixed in time.
For hosting providers, the problem is not only technical. It also affects service continuity, customer trust, and incident response. A mass reboot of servers may require coordination, but delaying mitigation on exposed systems may be more dangerous. The advantage of KernelCare, once the livepatch is available, will be precisely the ability to apply the fix without service interruption.
CloudLinux has indicated that patches will arrive within a short timeframe, with timing varying by product. On CloudLinux 9 and 10, patched AlmaLinux kernels are already appearing in testing repositories, although most production environments should normally wait for stable promotion unless operational risk requires faster action.
The message for administrators is clear: do not wait until the problem becomes visible in production. Local vulnerabilities are often exploited after an initial breach, and response time matters. The temporary mitigation is simple, but requires a reboot; the final patch is the correct long-term fix. Until then, every affected server should be inventoried, monitored, and covered by an action plan.
Frequently asked questions
What is CVE-2026-31431, or Copy Fail?
It is a local privilege escalation vulnerability in the Linux kernel related to algif_aead and the AF_ALG cryptographic interface. It can allow an unprivileged local user to gain root access.
Which CloudLinux versions are affected?
CloudLinux 7h, 8, 9, and 10 are affected. CloudLinux 7 is not affected, according to CloudLinux.
What is the recommended temporary mitigation?
CloudLinux recommends adding initcall_blacklist=algif_aead_init to the kernel boot parameters using grubby, then rebooting the server until the patched kernel or KernelCare livepatch is available.
Does Imunify360 replace the kernel patch?
No. Imunify360 adds detection and mitigation for known indicators, but CloudLinux stresses that it does not replace the kernel update or livepatch.
source: CloudLinux