2026-005: High Vulnerability in the Linux Kernel ("Copy Fail")
Linux kernel flaw CVE-2026-31431 ('Copy Fail', CVSS 7.8) allows unprivileged users to gain root via AF_ALG; a public PoC is out and most distros remain unpatched.
Disclosed on 29 April 2026, CVE-2026-31431 is a local privilege escalation in the Linux kernel's algif_aead module (AF_ALG crypto API), CVSS 7.8, stemming from a 2017 in-place optimisation. By chaining an AF_ALG socket operation with splice(), an unprivileged user can write 4 bytes into an arbitrary page-cache page, e.g. corrupting a setuid binary like /usr/bin/su to obtain a root shell. It affects virtually all kernels built since 2017, including Ubuntu 20.04-24.04, Amazon Linux 2023, RHEL 10.1, and SUSE 16; the mainline fix landed 1 April 2026 but no vendor packages were available as of 30 April. CERT-EU recommends the interim mitigation (disable algif_aead) and blocking AF_ALG via seccomp, prioritising Kubernetes nodes and CI/CD runners.
- CVE-2026-31431 (CVSS 7.8): local privilege escalation in the AF_ALG algif_aead module
- Chained AF_ALG + splice() yields a 4-byte arbitrary write to gain root via setuid binaries
- Affects kernels built since 2017; no distribution patches as of 30 April 2026
- Public PoC released at copy.fail; mitigation: disable algif_aead or block AF_ALG with seccomp
- Kubernetes nodes and CI/CD runners exposed to untrusted workloads are priority
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2026-31431 | Local Privilege Escalation (Copy Fail) in Linux Kernel algif_aead Interface CVE-2026-31431 ('Copy Fail') is an incorrect resource transfer between spheres (CWE-669/CWE-1288) in the Linux kernel's algif_aead implementation of the AF_ALG userspace crypto interface, introduced roughly nine years ago (around 2017, per public reporting) when commit 72548b093ee3 switched AEAD operations to in-place handling even though the source and destination buffers come from different mappings. A local, unprivileged user can trigger the flaw by performing AEAD operations through the AF_ALG socket interface, causing the kernel to mishandle the copy of ciphertext and associated data. Successful exploitation provides a reliable local privilege escalation to root (C:H/I:H/A:H per the CVSS vector). Nearly every major Linux distribution and enterprise platform is exposed, including the kernel itself, Red Hat Enterprise Linux (including AUS, EUS, TUS and Update Services for SAP Solutions), OpenShift Container Platform, Amazon Linux, Ubuntu, Debian, openSUSE Leap, SUSE CaaS Platform, NixOS, and Linux-based products from Arista and Siemens. The flaw has public proof-of-concept code, a 99.9% EPSS score, and was added to CISA's Known Exploited Vulnerabilities catalog on 2026-05-01, indicating exploitation in the wild (ransomware use is unknown). Do: Patch by installing the kernel update for CVE-2026-31431 through your distribution's security channel (Red Hat Enterprise Linux including AUS/EUS/TUS/SAP channels, OpenShift, Amazon Linux, Ubuntu, Debian, openSUSE Leap, SUSE CaaS Platform, NixOS, and Arista/Siemens firmware/software as applicable) and reboot into the patched kernel; the data provides no fixed version numbers, so defer to vendor advisories. Because the flaw is in CISA's KEV catalog (added 2026-05-01) with a 99.9% EPSS score, prioritize internet-reachable and multi-user systems first and follow BOD 22-01 guidance for cloud services. Check running kernel versions ('uname -r') and distribution advisory status to confirm you are on a fixed build. | 7.8 | 100% | KEV PoC ×5 |
| masshundreds of millions to billions of installations (servers, cloud instances, desktops, and Android/embedded devices running affected kernel generations) |
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Release Date: 30-04-2026 09:25:30
History:
- 29/04/2026 --- v1.0 -- Initial publication
Summary
On 29 April 2026, a high local privilege escalation vulnerability in the Linux kernel, tracked as CVE-2026-31431 and named "Copy Fail", was publicly disclosed [1].
The vulnerability affects every mainstream Linux distributions shipping a kernel built since 2017. A public proof-of-concept exploit has been released.
As of the date of this advisory, no distribution has shipped a fixed kernel package. The mainline fix was committed on 1 April 2026, but vendor updates are still pending across all major distributions. CERT-EU strongly recommends applying the interim mitigation immediately, prioritising Kubernetes nodes, and CI/CD runners exposed to untrusted workloads.
Technical Details
The vulnerability CVE-2026-31431, with a CVSS score of 7.8, is a local privilege escalation flaw in the Linux kernel's algif_aead module, the AEAD socket interface of the kernel's userspace crypto API (AF_ALG). The flaw originates from an in-place optimisation introduced in 2017 (commit 72548b093ee3), which allows page-cache pages to be placed into a writable destination scatterlist. By chaining an AF_ALG socket operation with splice(), an unprivileged local user can perform a controlled 4-byte write to an arbitrary page-cache-backed page, targeting a setuid binary such as /usr/bin/su to obtain a root shell [1].
The upstream fix is mainline commit a664bf3d603d, which reverts the 2017 optimisation. It was committed on 1 April 2026 [1].
Affected Products
The vulnerability affects every mainstream Linux distribution shipping a kernel built between 2017 and the availability of the patch. The following distributions were directly verified by the researchers [1]:
| Distribution | Kernel Version |
|---|---|
| Ubuntu 24.04 LTS | 6.17.0-1007-aws |
| Amazon Linux 2023 | 6.18.8-9.213.amzn2023 |
| RHEL 10.1 | 6.12.0-124.45.1.el10_1 |
| SUSE 16 | 6.12.0-160000.9-default |
Other distributions running kernels in the affected range are implicitly affected, including Debian, Arch Linux, Fedora, Rocky Linux, AlmaLinux, Oracle Linux, and embedded Linux distributions.
Patch availability by distribution (as of 30 April 2026):
| Distribution | Status |
|---|---|
| Ubuntu 20.04–24.04 | No fix available |
| Amazon Linux 2023 | No fix available |
| SUSE Linux Enterprise | No fix available |
| Red Hat Enterprise Linux | Status unknown |
Note: Ubuntu 26.04 (Resolute) and later kernels are not affected [2].
Additional information is available in the researcher's advisory [1] and in vendor security trackers [2,3,4].
Recommendations
CERT-EU strongly recommends applying the relevant kernel update as soon as possible once vendor patches become available, prioritising Kubernetes nodes and CI/CD runners.
Temporary Mitigation
Disable the algif_aead kernel module persistently on all affected systems until a patched kernel is available:
echo "install algif_aead /bin/false" > /etc/modprobe.d/disable-algif.conf rmmod algif_aead 2>/dev/null || true This workaround does not affect dm-crypt/LUKS, kTLS, IPsec/XFRM, OpenSSL, GnuTLS, NSS, or SSH. It may affect applications explicitly configured to use the afalg engine or that bind aead/skcipher/hash sockets directly. Exposure can be assessed with lsof | grep AF_ALG.
Hardening Containerised Environments and Pipelines
CERT-EU recommends blocking AF_ALG socket creation via seccomp policies on all containerised workloads and pipelines, regardless of patch status [1]. This applies to Docker and Podman-based environments [5] as well as Kubernetes clusters [6]. Since the exploit requires opening an AF_ALG socket as a first step, this measure effectively prevents exploitation even on unpatched kernels.
References
[2] https://ubuntu.com/security/CVE-2026-31431
[3] https://www.suse.com/security/cve/CVE-2026-31431
[4] https://access.redhat.com/security/cve/CVE-2026-31431
Text extracted automatically; images, tables and formatting may be missing. Original: https://cert.europa.eu/publications/security-advisories/2026-005/