CVE-2024-41096: Linux Kernel Use-After-Free Vulnerability

CVE-2024-41096 Overview

CVE-2024-41096 is a use-after-free vulnerability in the Linux kernel's PCI/MSI (Peripheral Component Interconnect / Message Signaled Interrupts) subsystem, specifically within the msi_capability_init function. The vulnerability was identified through KFENCE (Kernel Electric-Fence), a low-overhead memory safety error detector in the Linux kernel. This flaw occurs when MSI descriptor allocation fails during the IRQ domain allocation process, leading to a freed memory access in the error handling path.

Critical Impact

Local attackers with low privileges can potentially achieve code execution or cause system crashes by triggering the use-after-free condition during PCI device initialization, impacting system confidentiality, integrity, and availability.

Affected Products

• Linux Kernel (various versions)
• Debian Linux (as referenced in LTS announcements)
• Systems utilizing PCI/MSI interrupt handling

Discovery Timeline

• July 29, 2024 - CVE-2024-41096 published to NVD
• November 3, 2025 - Last updated in NVD database

Technical Details for CVE-2024-41096

Vulnerability Analysis

This use-after-free vulnerability occurs in the PCI/MSI initialization code path when setting up Message Signaled Interrupts. The core issue manifests when the __msi_domain_alloc_locked() function fails during IRQ allocation. When this failure occurs, the MSI descriptor memory is freed through msi_domain_free_locked(), but the error handling code in msi_capability_init() subsequently attempts to access this freed descriptor for performing unmask operations.

The vulnerability specifically affects the __pci_enable_msi_range() function, which is called when PCI drivers attempt to allocate interrupt vectors using functions like pci_alloc_irq_vectors() or pci_alloc_irq_vectors_affinity(). The memory allocated by msi_alloc_desc() during descriptor setup becomes dangerously accessible after being freed, creating a classic use-after-free condition.

Root Cause

The root cause lies in the error handling logic within msi_capability_init(). When MSI IRQ allocation fails in __msi_domain_alloc_locked(), the failure triggers msi_domain_free_locked() which frees the MSI descriptor. However, the error exit path in pci_msi_setup_msi_irqs() still attempts to access the descriptor to perform unmasking operations, accessing memory that has already been returned to the kernel memory allocator.

The fix addresses this by copying the descriptor data before the allocation attempt. This copy is then used for the unmask operation in the error exit path, ensuring that valid memory is accessed regardless of whether the original descriptor has been freed.

Attack Vector

This vulnerability requires local access to the system with low privileges. An attacker could potentially exploit this by triggering PCI device initialization scenarios that cause the MSI allocation to fail, forcing the vulnerable error handling path to execute. The attack vector involves manipulating or interacting with PCI device enumeration in a way that causes __msi_domain_alloc_locked() to fail, subsequently triggering the use-after-free read.

The vulnerability was detected by KFENCE with the following characteristics: the memory was allocated from a 104-byte object in the kmalloc-128 cache, and the use-after-free read occurred approximately 3.3 milliseconds after the memory was freed.

Detection Methods for CVE-2024-41096

Indicators of Compromise

• KFENCE error messages in kernel logs indicating use-after-free in __pci_enable_msi_range
• Kernel panic or crash dumps referencing msi_capability_init or related MSI functions
• Unexpected system instability during PCI device initialization or driver loading

Detection Strategies

• Enable KFENCE in kernel builds to detect memory safety violations during runtime
• Monitor kernel logs for BUG or WARNING messages related to PCI/MSI subsystem
• Deploy SentinelOne agents with kernel-level monitoring capabilities to detect anomalous memory access patterns

Monitoring Recommendations

• Configure continuous kernel log monitoring for KFENCE-related error messages
• Implement alerting for kernel oops or panics involving MSI-related function names in the call stack
• Use SentinelOne's endpoint detection and response (EDR) capabilities to identify potential exploitation attempts targeting kernel memory corruption vulnerabilities

How to Mitigate CVE-2024-41096

Immediate Actions Required

• Update affected Linux kernel installations to patched versions as soon as available
• Monitor vendor security advisories for distribution-specific kernel updates
• Consider enabling KFENCE on production systems to detect similar memory safety issues

Patch Information

The Linux kernel maintainers have released patches to address this vulnerability. The fix involves creating a copy of the MSI descriptor data before the allocation attempt, which is then used for unmask operations in the error exit path. This ensures that the error handling code never accesses freed memory.

The following kernel commits contain the fix:

• Linux Kernel Commit 45fc8d20
• Linux Kernel Commit 9eee5330
• Linux Kernel Commit ff1121d2
• Linux Kernel Commit 0ae40b2d

Debian users should refer to the Debian LTS Announcement January 2025 for distribution-specific updates.

Workarounds

• Limit local user access to reduce the attack surface until patches can be applied
• Monitor PCI device initialization for anomalies using kernel tracing tools
• Consider restricting driver loading capabilities for non-administrative users where feasible
• Enable kernel hardening features such as KASLR and SMEP/SMAP to increase exploitation difficulty

# Check current kernel version for vulnerability assessment
uname -r

# Verify if KFENCE is enabled in current kernel
cat /sys/kernel/debug/kfence/stats 2>/dev/null || echo "KFENCE not available"

# Monitor kernel logs for MSI-related errors
dmesg | grep -i "msi\|kfence"