CVE-2026-46098: Linux Kernel Use-After-Free Vulnerability

CVE-2026-46098 Overview

CVE-2026-46098 is a use-after-free vulnerability in the Linux kernel's Communication CPU Application Interface (CAIF) networking subsystem. The flaw resides in the client teardown path, where caif_connect() can dismantle an existing client following a remote shutdown. The function calls caif_disconnect_client() and then caif_free_client(), releasing the service layer referenced by adap_layer->dn but leaving the pointer stale. When the socket is later destroyed, caif_sock_destructor() invokes caif_free_client() again and dereferences the freed service object.

Critical Impact
Repeated teardown of CAIF clients dereferences a freed service layer pointer, leading to kernel memory corruption and potential local denial of service or privilege escalation.

Affected Products

Linux kernel (mainline) prior to the fix commits referenced in stable trees
Linux kernel stable branches receiving the backported patches
Distributions shipping kernels with the CAIF networking subsystem enabled

Discovery Timeline

2026-05-27 - CVE-2026-46098 published to NVD
2026-05-27 - Last updated in NVD database

Technical Details for CVE-2026-46098

Vulnerability Analysis

The vulnerability is a use-after-free condition in the CAIF socket layer of the Linux kernel networking stack. CAIF provides communication channels between modem applications and an external modem. The bug stems from improper lifecycle management of the service layer pointer associated with a CAIF client adaptation layer.

When a remote peer initiates shutdown, caif_connect() tears down the previous client by calling caif_disconnect_client() followed by caif_free_client(). The free routine releases the service object referenced through adap_layer->dn but does not clear the pointer. The stale reference remains accessible from the socket state.

At socket destruction, caif_sock_destructor() calls caif_free_client() a second time. This second invocation dereferences the already-freed memory, producing a classic use-after-free [CWE-416].

Root Cause

The root cause is missing pointer clearing after deallocation. caif_free_client() releases the kernel object pointed to by adap_layer->dn without nulling out the reference or removing the client/service linkage. Subsequent teardown paths assume the pointer is either valid or NULL, but it is neither — it points to released memory.

Attack Vector

A local attacker with the ability to open CAIF sockets can trigger the unsafe teardown sequence by inducing a remote shutdown followed by socket destruction. Successful exploitation corrupts kernel heap state, which can lead to denial of service through kernel panic or, depending on heap layout and allocator behavior, escalation to arbitrary kernel memory writes.

The vulnerability requires that the CAIF subsystem be loaded and reachable from the attacker's context. The fix clears the client and service links before releasing the service object, making repeated teardown a no-op. Refer to the kernel commit a4b191ddc12c and related stable backports for the implementation.

Detection Methods for CVE-2026-46098

Indicators of Compromise

Kernel oops or panic messages referencing caif_free_client, caif_sock_destructor, or cfctrl symbols in dmesg and /var/log/kern.log
KASAN use-after-free reports identifying the CAIF code paths on debug kernels
Unexpected process crashes or kernel taints on hosts that load the caif module

Detection Strategies

Audit loaded kernel modules with lsmod | grep caif to identify systems exposing the vulnerable code path
Compare running kernel versions against vendor advisories to confirm whether the fix commits are present
Enable KASAN on test kernels to surface use-after-free patterns during fuzzing of the CAIF socket family

Monitoring Recommendations

Forward kernel ring buffer logs to a centralized logging platform and alert on segfaults, oops, or BUG messages referencing networking subsystems
Track kernel version inventory across the Linux fleet to verify patch deployment status
Monitor for unexpected socket family usage (AF_CAIF, family 37) by unprivileged processes on systems where CAIF is not required

How to Mitigate CVE-2026-46098

Immediate Actions Required

Apply the upstream patches that clear the client and service pointers before releasing the service object, available in the referenced stable kernel commits
Update to a distribution kernel package that incorporates the CAIF teardown fix
Where patching is delayed, blacklist the caif kernel module on systems that do not require CAIF connectivity

Patch Information

The fix is contained in the following kernel commits across mainline and stable branches: 3ac6db584d9d, 63d21a3aa010, 914c6456fcfc, a4b191ddc12c, and f7cf8ece8cee. The patch nulls the relevant client/service references in caif_free_client() so repeated invocation no longer dereferences freed memory.

Workarounds

Prevent the caif module from loading by adding blacklist caif to a file under /etc/modprobe.d/ on systems that do not need it
Restrict creation of AF_CAIF sockets to privileged users through seccomp or LSM policies where supported
Limit local user access on multi-tenant Linux hosts until patched kernels are deployed

bash

# Configuration example
echo 'blacklist caif' | sudo tee /etc/modprobe.d/blacklist-caif.conf
sudo rmmod caif 2>/dev/null || true