CVE-2023-1077: Linux Kernel Privilege Escalation Flaw

CVE-2023-1077 Overview

CVE-2023-1077 is a type confusion vulnerability [CWE-843] in the Linux kernel's real-time (RT) scheduler. The flaw resides in the pick_next_rt_entity() function, which may return a type-confused entry that the BUG_ON sanity check fails to detect. The confused entry is not NULL but a list_head, which the scheduler then treats as a sched_rt_entity, leading to memory corruption.

The vulnerability affects the upstream Linux kernel, Debian Linux 10, and multiple NetApp storage appliance firmware images including the A700s, A400, C400, 8300, 8700, and the H-series HCI nodes.

Critical Impact
A local authenticated attacker can trigger memory corruption in the kernel scheduler, potentially leading to privilege escalation, kernel crashes, or compromise of confidentiality, integrity, and availability on affected systems.

Affected Products

Linux Kernel (multiple versions prior to the upstream fix in commit 7c4a5b89a0b5)
Debian Linux 10
NetApp storage appliances: A700s, A400, C400, 8300, 8700, H300S, H500S, H700S, H410S, H410C

Discovery Timeline

2023-03-27 - CVE-2023-1077 published to the National Vulnerability Database
2023-05-11 - NetApp publishes security advisory NTAP-20230511-0002
2023-05 - Debian LTS announces fix for affected packages
2024-01 - Additional Debian LTS update issued
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-1077

Vulnerability Analysis

The vulnerability is a kernel type confusion [CWE-843] in the Completely Fair Scheduler's real-time class. The pick_next_rt_entity() function selects the next runnable real-time task from the run queue. Under specific conditions, the function returns a pointer that does not point to a valid sched_rt_entity structure but instead references a list_head element within the queue.

The existing BUG_ON assertion only checks whether the returned pointer is NULL. Because the confused entry is non-NULL, the check passes and the kernel proceeds to dereference the pointer as if it were a sched_rt_entity. Adjacent memory is then interpreted using the wrong structure layout, producing memory corruption inside privileged kernel context.

Exploitation requires local access with low privileges and high attack complexity. Successful exploitation can corrupt scheduler state, induce kernel panics, or be leveraged for local privilege escalation.

Root Cause

The root cause is an insufficient sanity check in pick_next_rt_entity(). The function relies on a BUG_ON(!entity) style guard that detects only null returns. It does not verify that the returned object is actually a sched_rt_entity rather than a sibling list_head node embedded in the same data structure. This violates the type contract that downstream scheduler code depends on.

Attack Vector

A local user with the ability to create real-time scheduling tasks or influence RT run queue state can trigger the buggy code path. The attack requires precise timing and scheduler manipulation, accounting for the high attack complexity. Once triggered, the kernel operates on attacker-influenced memory as if it were a valid scheduling entity, opening a path to memory corruption primitives usable for privilege escalation.

No public proof-of-concept exploit has been published, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. The vulnerability mechanism is documented in the upstream kernel fix referenced in the Kernel Commit 7c4a5b.

Detection Methods for CVE-2023-1077

Indicators of Compromise

Unexpected kernel oops or panic messages referencing pick_next_rt_entity, sched_rt_entity, or RT run queue functions in dmesg and /var/log/kern.log
Sudden process scheduling anomalies, stalls, or crashes on systems with workloads using SCHED_FIFO or SCHED_RR policies
Local processes attempting to set real-time scheduling priorities via sched_setscheduler() or chrt followed by system instability

Detection Strategies

Audit installed kernel versions against the fixed versions listed in the upstream commit and vendor advisories from Debian and NetApp
Monitor kernel ring buffer logs for warnings, BUG, or oops messages originating from kernel/sched/rt.c
Track use of real-time scheduling syscalls by non-privileged users using auditd rules on sched_setscheduler and sched_setattr

Monitoring Recommendations

Forward kernel logs to a centralized log management platform and alert on scheduler-related panics
Inventory NetApp ONTAP and HCI firmware versions and compare against NetApp Security Advisory NTAP-20230511-0002
Establish a baseline for legitimate RT scheduling activity and alert on anomalous use by user-space processes

How to Mitigate CVE-2023-1077

Immediate Actions Required

Apply the upstream Linux kernel patch from commit 7c4a5b89a0b5 or update to a kernel version that includes the fix
Update Debian 10 systems using the packages listed in the Debian LTS Announcement May 2023 and the Debian LTS Announcement January 2024
Upgrade affected NetApp firmware according to NetApp Security Advisory NTAP-20230511-0002
Restrict local shell access to trusted users on systems that cannot be patched immediately

Patch Information

The upstream fix is available in the Linux kernel via commit 7c4a5b89a0b5a57a64b601775b296abf77a9fe97. The patch corrects the type confusion in pick_next_rt_entity() so that the scheduler no longer returns a list_head pointer mistakenly treated as a sched_rt_entity. Distribution-specific patches have been released by Debian for affected LTS packages, and NetApp has issued firmware updates for impacted storage appliances.

Workarounds

Limit the ability of unprivileged users to assign real-time scheduling priorities by tightening RLIMIT_RTPRIO and RLIMIT_RTTIME via /etc/security/limits.conf
Disable or restrict access to real-time scheduling policies (SCHED_FIFO, SCHED_RR) for non-administrative accounts where operationally feasible
Reduce local attack surface by removing shell access for non-essential users on affected hosts until patches are applied

bash

# Verify running kernel version on Linux hosts
uname -r

# Check for the fixed package on Debian-based systems
dpkg -l | grep linux-image
apt-get update && apt-get install --only-upgrade linux-image-$(uname -r | sed 's/[^-]*-[^-]*-//')

# Restrict real-time scheduling for non-root users (limits.conf)
# Append to /etc/security/limits.conf:
# *    hard    rtprio    0
# *    hard    nice      0