CVE-2023-3268: Linux Kernel Privilege Escalation Flaw

CVE-2023-3268 Overview

CVE-2023-3268 is an out-of-bounds (OOB) memory access flaw in the Linux kernel's relayfs subsystem. The vulnerability resides in the relay_file_read_start_pos function within kernel/relay.c. A local attacker with low privileges can trigger the flaw to crash the system or leak kernel internal information. The defect is classified under CWE-125: Out-of-bounds Read.

The Linux kernel project addressed the issue in version 6.3.2 via commit 43ec16f1450f4936025a9bdf1a273affdb9732c1. Debian shipped fixes through DSA-5448 and DSA-5480 for affected Debian 10, 11, and 12 releases.

Critical Impact
Local attackers can crash the kernel or read out-of-bounds memory from kernel/relay.c, enabling denial of service and disclosure of sensitive kernel data such as pointers used to bypass KASLR.

Affected Products

Linux kernel versions prior to 6.3.2
Debian Linux 10, 11, and 12
NetApp products referenced in advisory NTAP-20230824-0006

Discovery Timeline

2023-06-16 - CVE-2023-3268 published to NVD
2023-07 - Debian LTS advisory released for affected packages
2023-10 - Additional Debian LTS advisory issued
2025-03-11 - Last updated in NVD database

Technical Details for CVE-2023-3268

Vulnerability Analysis

The Linux kernel relay interface (relayfs) provides an efficient mechanism for transferring large amounts of data from kernel space to user space through per-CPU ring buffers. Subsystems such as tracing, debugging facilities, and blktrace rely on relayfs for log streaming.

The flaw resides in relay_file_read_start_pos, which calculates the read position into a relay buffer based on the file offset supplied by user space. When the computed position exceeds the bounds of the underlying subbuffer array, the function dereferences memory outside the allocated region. The result is either a kernel crash via invalid pointer access or disclosure of adjacent kernel memory contents back to the requesting reader.

Exploitation requires only local access and the ability to open and read from a relayfs-backed file, such as those exposed under debugfs. The defect impacts confidentiality and availability but does not permit modification of kernel data.

Root Cause

The root cause is insufficient validation of the read position against the subbuffer count before indexing into the per-CPU buffer array. When the file pointer crosses past the last valid subbuffer, the index used in subsequent arithmetic produces an out-of-range value that the function does not clamp. The upstream fix in commit 43ec16f corrects the position calculation so the read offset is bounded by the channel's actual subbuffer count.

Attack Vector

A local user with permission to open a relay-backed file performs read() or lseek() operations crafted to drive the internal position past the end of the relay channel. Repeated reads then trigger the out-of-bounds access. Access to debugfs mounts, where relay files are commonly exposed, is typically restricted to root, but kernel configurations or container deployments that loosen these restrictions broaden the attack surface.

The vulnerability does not require user interaction and can be exploited via local code execution paths, including scripts running under low-privileged accounts that have read access to a relayfs node.

The vulnerability manifests in the relay buffer position arithmetic. See the Linux Kernel Commit 43ec16f and the Kernel Mailing List Discussion for the patch details and original analysis.

Detection Methods for CVE-2023-3268

Indicators of Compromise

Unexpected kernel oops or panic entries in dmesg or /var/log/kern.log referencing relay_file_read_start_pos or kernel/relay.c.
Repeated read() or lseek() syscalls from unprivileged processes against files under debugfs relay channels.
Process crashes or segmentation events accompanied by kernel address leakage in user-visible buffers.

Detection Strategies

Audit kernel versions across the fleet and flag Linux hosts running kernels earlier than 6.3.2 without distribution backports.
Monitor auditd EXECVE and PATH records for non-root processes accessing /sys/kernel/debug relay files.
Correlate kernel ring buffer warnings with the originating process and user context to identify probing activity.

Monitoring Recommendations

Forward dmesg and audit logs to a centralized SIEM for retention and alerting on relay-related kernel warnings.
Track package inventory for linux-image-* versions on Debian 10, 11, and 12 systems against the fixed builds in DSA-5448 and DSA-5480.
Alert on unusual user activity that mounts or interacts with debugfs, which is the most common surface for relay files.

How to Mitigate CVE-2023-3268

Immediate Actions Required

Upgrade the Linux kernel to version 6.3.2 or later, or apply the distribution backport that includes commit 43ec16f1450f4936025a9bdf1a273affdb9732c1.
Apply Debian security updates from DSA-5448 and DSA-5480 on Debian 10, 11, and 12 hosts.
Review NetApp environments against advisory NTAP-20230824-0006 and apply vendor-supplied fixes.

Patch Information

The upstream fix is included in the Linux 6.3.2 ChangeLog and applied via the Linux Kernel Commit 43ec16f. Debian users should install kernel packages aligned with the Debian LTS Announcement July 2023 or the Debian LTS Announcement October 2023.

Workarounds

Restrict access to debugfs by unmounting it on production hosts that do not require kernel debugging interfaces.
Enforce strict permissions on relay-backed files so only root can open them, reducing exposure to local users.
Limit container and sandbox capabilities such as CAP_SYS_ADMIN to prevent unprivileged workloads from interacting with relay channels.

bash

# Verify the running kernel version and remediation status
uname -r

# Debian: install kernel updates and reboot
sudo apt-get update && sudo apt-get install --only-upgrade linux-image-$(uname -r | sed 's/.*-//')
sudo systemctl reboot

# Unmount debugfs where it is not required
sudo umount /sys/kernel/debug

# Prevent debugfs auto-mount by removing it from /etc/fstab
sudo sed -i '/debugfs/d' /etc/fstab