CVE-2023-6931: Linux Kernel Privilege Escalation Flaw

CVE-2023-6931 Overview

CVE-2023-6931 is a heap out-of-bounds write vulnerability in the Linux kernel's Performance Events (perf_events) subsystem. The flaw resides in the perf_read_group() function, where a perf_event's read_size value can overflow. This overflow leads to an out-of-bounds increment or write on the kernel heap. A local, authenticated attacker can exploit this condition to achieve local privilege escalation on affected Linux systems. The vulnerability affects the upstream Linux kernel and downstream distributions including Debian Linux. It is classified under CWE-787 (Out-of-Bounds Write) and was addressed in upstream commit 382c27f4ed28f803b1f1473ac2d8db0afc795a1b.

Critical Impact
Local attackers with low privileges can corrupt kernel heap memory and escalate to root, compromising confidentiality, integrity, and availability of the host.

Affected Products

Linux Kernel (versions prior to the fix commit 382c27f4ed28f803b1f1473ac2d8db0afc795a1b)
Debian Linux 10.0
Siemens industrial products incorporating affected Linux kernels (see vendor advisories SSA-265688, SSA-398330, SSA-613116, SSA-794697)

Discovery Timeline

2023-12-19 - CVE-2023-6931 published to NVD
2026-05-12 - Last updated in NVD database

Technical Details for CVE-2023-6931

Vulnerability Analysis

The vulnerability exists in the Linux kernel's Performance Events subsystem, which exposes the perf_event_open() syscall to userspace for performance monitoring. When an event group is read through perf_read_group(), the kernel calculates a read_size value used to size the output buffer and drive iteration over sibling events. An arithmetic overflow in this size calculation causes the kernel to write or increment counters beyond the bounds of the allocated heap object. Because the corruption occurs in kernel-managed slab memory, an attacker who controls adjacent allocations can shape the heap to overwrite security-sensitive structures and pivot to arbitrary kernel write primitives.

Root Cause

The root cause is unchecked arithmetic when computing read_size for a perf_event group. The product of the number of group siblings and per-event size fields can exceed the bounds of the integer type used, producing a truncated or otherwise incorrect size. The kernel then proceeds with heap accesses based on this corrupted size, violating the allocation boundary. The upstream fix in commit 382c27f4ed28f803b1f1473ac2d8db0afc795a1b introduces overflow-safe size computation in the perf events code path.

Attack Vector

Exploitation requires local access and the ability to invoke perf_event_open(). The attacker constructs a crafted event group with parameters that cause read_size to overflow. Reading the group then triggers the out-of-bounds write in kernel heap memory. With careful heap grooming, this primitive can be converted into a privilege escalation, granting root on the target host. The attack complexity is rated high because reliable exploitation requires kernel heap layout manipulation and bypassing modern kernel hardening features such as SMAP, SMEP, and KASLR.

No public proof-of-concept exploit code has been published in the enriched data for this CVE. Refer to the upstream Linux Kernel Commit Update and the Kernel Dance Commit Overview for the authoritative technical details of the fix.

Detection Methods for CVE-2023-6931

Indicators of Compromise

Unexpected kernel oops or panic messages in dmesg referencing perf_read_group, perf_event, or slab corruption.
Processes invoking perf_event_open() from unprivileged users outside of legitimate profiling workflows.
New root shells or setuid activity originating from previously unprivileged user sessions.
KASAN or slab debug reports indicating out-of-bounds writes within kernel/events/core.c.

Detection Strategies

Audit kernel package versions against the patched baselines published by your distribution and compare against commit 382c27f4ed28f803b1f1473ac2d8db0afc795a1b.
Monitor auditd for perf_event_open syscalls correlated with subsequent privilege changes or unusual child process spawning.
Enable kernel hardening features such as kernel.perf_event_paranoid=3 and alert on attempts to lower it.

Monitoring Recommendations

Forward auditd, dmesg, and kernel ring buffer logs to a centralized SIEM for retention and correlation.
Establish baselines for legitimate perf_event_open() callers and alert on deviations from non-developer accounts.
Track privilege escalation patterns: unprivileged process followed by UID transition to 0 within a short window.

How to Mitigate CVE-2023-6931

Immediate Actions Required

Apply vendor kernel updates that include upstream commit 382c27f4ed28f803b1f1473ac2d8db0afc795a1b and reboot affected hosts.
For Debian systems, install the kernel updates referenced in the Debian LTS Security Notice and follow-up notice.
For Siemens industrial environments, follow guidance in the Siemens Product Security Advisory SSA-265688 and related bulletins (SSA-398330, SSA-613116, SSA-794697).
Inventory all Linux hosts and prioritize multi-tenant systems, build servers, and CI/CD runners where local users are most prevalent.

Patch Information

The vulnerability is fixed by upstream commit 382c27f4ed28f803b1f1473ac2d8db0afc795a1b, which corrects the overflow in perf_read_group(). Distribution-specific patched packages are available via the Linux Kernel Commit Update and downstream advisories from Debian and Siemens. Apply the patched kernel and reboot to load the corrected code path.

Workarounds

Restrict access to perf_event_open() by setting kernel.perf_event_paranoid=3 via sysctl, which limits unprivileged use of performance events.
Limit shell access on sensitive hosts and enforce least privilege so untrusted users cannot invoke the affected syscall.
Where supported, enable Linux Security Modules (SELinux, AppArmor) policies that constrain perf_event_open() to specific authorized binaries.

bash

# Configuration example: restrict unprivileged access to perf_event_open()
echo 'kernel.perf_event_paranoid = 3' | sudo tee /etc/sysctl.d/10-perf-restrict.conf
sudo sysctl --system

# Verify the runtime value
sysctl kernel.perf_event_paranoid

# Confirm the running kernel includes the fix commit
uname -r