CVE-2024-53057: Linux Kernel Use-After-Free Vulnerability

CVE-2024-53057 Overview

CVE-2024-53057 is a Use-After-Free (UAF) vulnerability in the Linux kernel's network scheduler (net/sched) subsystem. The vulnerability exists in the qdisc_tree_reduce_backlog function within net/sched/sch_api.c, where an incorrect assumption about qdisc major handles leads to a dangling class pointer condition. Specifically, qdiscs with major handle ffff: were incorrectly assumed to be either root or ingress, but egress qdiscs can also be legitimately created with this handle. For qdiscs like DRR (Deficit Round Robin) that maintain an active class list, this flawed logic results in a UAF vulnerability with a dangling class pointer.

Critical Impact

Local attackers with low privileges can exploit this UAF vulnerability to potentially achieve code execution with elevated privileges, compromise system integrity, or cause denial of service through kernel memory corruption.

Affected Products

• Linux Kernel versions prior to patched releases
• Linux Kernel 6.12 release candidates (rc1 through rc5)
• Various stable kernel branches requiring backported patches

Discovery Timeline

• 2024-11-19 - CVE-2024-53057 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-53057

Vulnerability Analysis

This vulnerability stems from a logic error in the kernel's traffic control (TC) subsystem. The qdisc_tree_reduce_backlog function is responsible for propagating backlog updates through the qdisc hierarchy when packets are dropped or dequeued. The function uses a condition to determine when to stop iterating up the qdisc tree.

The original implementation assumed that any qdisc with a major handle of ffff: must be either the root qdisc or the ingress qdisc, and would stop iteration based on this assumption. However, this assumption is incorrect because it is entirely valid to create egress qdiscs with the ffff: major handle.

When a hierarchical qdisc like DRR (Deficit Round Robin) maintains an active class list and an egress qdisc with major handle ffff: exists in the tree, the incorrect termination condition causes the function to stop prematurely or continue incorrectly. This leads to a Use-After-Free condition where a class pointer becomes dangling after the associated memory has been freed, but the pointer is still accessed.

Root Cause

The root cause is a flawed termination condition in qdisc_tree_reduce_backlog. The fix identified in commit 066a3b5b2346 originally aimed to avoid iterating over the ingress qdisc (whose parent is itself) by checking for the ffff: major handle. However, this check was overly broad and incorrectly captured egress qdiscs that legitimately use the ffff: major handle.

The proper fix changes the termination condition to stop when TC_H_ROOT is reached instead of checking for the ffff: major handle. The ingress qdisc can only be retrieved when a hierarchy without a ffff: major handle calls qdisc_lookup with TC_H_MAJ(TC_H_ROOT). This ensures that updates properly propagate through all tree levels, including egress qdiscs with ffff: major handles, and correctly terminate at TC_H_ROOT.

Attack Vector

The vulnerability requires local access to the system with the ability to configure traffic control qdiscs. An attacker would need:

1. Local access to the target Linux system
2. Low-level privileges sufficient to create and manipulate network qdiscs
3. The ability to create an egress qdisc with the ffff: major handle
4. Triggering backlog reduction operations on hierarchical qdiscs like DRR that maintain active class lists

The attack exploits the race condition and memory management flaw to access freed memory, potentially allowing arbitrary code execution in kernel context or causing system instability.

Detection Methods for CVE-2024-53057

Indicators of Compromise

• Kernel panic or oops messages referencing qdisc_tree_reduce_backlog or sch_api.c
• Unexpected system crashes during network traffic control operations
• Memory corruption indicators in kernel logs related to the net/sched subsystem

Detection Strategies

• Monitor kernel logs for UAF-related warnings or KASAN (Kernel Address Sanitizer) reports in the net/sched code path
• Implement kernel auditing for traffic control configuration changes, particularly qdisc creation with major handle ffff:
• Deploy runtime kernel protection mechanisms that can detect memory corruption attempts

Monitoring Recommendations

• Enable KASAN in development and testing environments to detect memory safety violations
• Monitor for suspicious traffic control configurations using tc command auditing
• Implement system call monitoring for setsockopt and netlink operations related to qdisc manipulation

How to Mitigate CVE-2024-53057

Immediate Actions Required

• Apply the kernel patch from the official Linux kernel stable branches immediately
• Restrict access to traffic control configuration to trusted administrators only
• Monitor systems for signs of exploitation attempts through kernel log analysis
• Consider temporarily disabling complex qdisc configurations if patching is delayed

Patch Information

The vulnerability has been resolved through multiple kernel commits across different stable branches. The fix modifies a single line in net/sched/sch_api.c to change the termination condition from checking for the ffff: major handle to properly checking for TC_H_ROOT.

Available patches:

• Linux Kernel Commit 05df1b1
• Linux Kernel Commit 2e95c43
• Linux Kernel Commit 580b318
• Linux Kernel Commit 597cf97
• Linux Kernel Commit 9995909
• Linux Kernel Commit ce691c8
• Linux Kernel Commit dbe778b
• Linux Kernel Commit e7f9a6f

Distribution-specific advisories have been released, including Debian LTS Announcement January 2025 and Debian LTS Announcement March 2025.

Workarounds

• Restrict access to network namespace and traffic control capabilities using capabilities management (CAP_NET_ADMIN)
• Implement SELinux or AppArmor policies to limit qdisc configuration to trusted processes
• Avoid using complex hierarchical qdisc configurations with DRR or similar qdiscs until patched
• Use network namespaces to isolate untrusted workloads from traffic control configurations

# Restrict traffic control capabilities to root only
# Verify current kernel version
uname -r

# Check for available kernel updates
apt update && apt list --upgradable | grep linux-image

# Apply kernel updates (Debian/Ubuntu)
apt upgrade linux-image-$(uname -r | cut -d- -f1-2)

# Reboot to apply the patched kernel
systemctl reboot