CVE-2026-52972: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-52972 Overview

CVE-2026-52972 is a vulnerability in the Linux kernel's crypto/af_alg subsystem. The flaw stems from missing bounds checking on the Authenticated Encryption with Associated Data (AEAD) associated data length. Without a cap, arithmetic operations used to validate the TX buffer size can overflow. The upstream fix caps the associated data length to 0x80000000 to prevent integer overflow during TX buffer size checks.

The vulnerability affects the AF_ALG userspace crypto interface, which exposes kernel cryptographic transforms to unprivileged processes via a socket API. Multiple stable kernel branches received backported patches.

Critical Impact
Unbounded AEAD associated data length can cause arithmetic overflow in TX buffer size validation, potentially leading to memory corruption or denial of service within the kernel crypto subsystem.

Affected Products

Linux kernel crypto/af_alg subsystem (mainline)
Linux stable kernel branches receiving backports referenced in the upstream commits
Distributions shipping the Linux kernel with the AF_ALG userspace crypto interface enabled

Discovery Timeline

2026-06-24 - CVE-2026-52972 published to NVD
2026-06-24 - Last updated in NVD database

Technical Details for CVE-2026-52972

Vulnerability Analysis

The Linux kernel exposes kernel-mode cryptographic transforms to userspace through AF_ALG, a socket family defined in crypto/af_alg.c. Applications use this interface for symmetric ciphers, hashes, and AEAD operations such as AES-GCM. AEAD operations accept both plaintext and an associated data (AD) buffer that is authenticated but not encrypted.

Before the fix, the kernel did not impose an upper bound on the AD length supplied through control messages. Arithmetic that combined the AD length with other size fields to validate the TX buffer could wrap around when the AD length approached SIZE_MAX. The patch caps the AD length to 0x80000000, ensuring the subsequent size calculations remain within a safe range.

Root Cause

The root cause is an integer overflow [CWE-190] in the TX buffer size validation path of the AEAD code in af_alg. Untrusted size values from user-controlled control messages were used in arithmetic without bounds checking, allowing the computed buffer size to underflow or wrap.

Attack Vector

A local user with permission to open an AF_ALG socket can submit AEAD requests with a crafted associated data length. The malformed length triggers the overflow during TX buffer size validation. The exact impact depends on how the corrupted size value is consumed downstream, but the upstream fix is framed as defense against arithmetic overflow rather than a confirmed exploitation primitive. No public exploit is available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. The EPSS probability is 0.18%.

The vulnerability manifests in the AEAD send path of af_alg. See the upstream commits for the precise code change.

Detection Methods for CVE-2026-52972

Indicators of Compromise

No public indicators of compromise are associated with CVE-2026-52972 at the time of publication.
Unexpected kernel oops or warnings referencing af_alg or AEAD operations in dmesg and /var/log/kern.log may indicate exploitation attempts against unpatched kernels.

Detection Strategies

Inventory Linux hosts and compare running kernel versions against the patched stable releases referenced in the upstream commits.
Audit which workloads open AF_ALG sockets, as legitimate use is limited to applications relying on the kernel crypto API from userspace.
Alert on processes invoking socket(AF_ALG, ...) from contexts that historically do not use kernel crypto offload.

Monitoring Recommendations

Enable kernel auditing (auditd) for socket syscalls with the AF_ALG family to baseline normal usage.
Monitor for kernel crashes, KASAN reports, or WARN_ON events that reference the crypto subsystem.
Track package and kernel update status across the fleet to confirm the patched version is deployed.

How to Mitigate CVE-2026-52972

Immediate Actions Required

Apply the Linux stable kernel update that contains the af_alg AD length cap once available for your distribution.
Reboot hosts after the kernel package upgrade so the new image is loaded.
Restrict local access on multi-tenant systems where untrusted users could open AF_ALG sockets.

Patch Information

The fix caps the AEAD associated data length to 0x80000000 in crypto/af_alg. The change has been merged and backported across multiple stable branches. Reference the upstream commits: Kernel commit 265ac26, Kernel commit 9794890, Kernel commit a1c5672, Kernel commit a4fe4eb, Kernel commit a9f68d9, Kernel commit e4c4a50, and Kernel commit f8a5203.

Workarounds

If AF_ALG is not required, disable the CONFIG_CRYPTO_USER_API family of kernel options in custom builds and rebuild the kernel.
On systems using systemd, restrict the AF_ALG socket family for untrusted services via RestrictAddressFamilies= in unit files.
Use seccomp filters to block the socket syscall with the AF_ALG family in sandboxed workloads that do not need kernel crypto offload.

bash

# Example: restrict AF_ALG for a systemd service
# /etc/systemd/system/myservice.service.d/hardening.conf
[Service]
RestrictAddressFamilies=AF_UNIX AF_INET AF_INET6
SystemCallFilter=~@privileged