CVE-2024-41096 Overview
CVE-2024-41096 is a use-after-free vulnerability [CWE-416] in the Linux kernel's PCI/MSI (Message Signaled Interrupts) subsystem. The flaw resides in the msi_capability_init() function, where the error exit path accesses a Message Signaled Interrupt (MSI) descriptor that has already been freed. KFENCE memory safety detection identified the issue during __pci_enable_msi_range() execution. A local authenticated attacker who can trigger MSI allocation failure paths may exploit the freed descriptor to corrupt kernel memory.
Critical Impact
Exploitation can lead to kernel memory corruption, local privilege escalation, or denial of service on affected Linux systems running vulnerable kernel versions.
Affected Products
- Linux Kernel (multiple stable branches prior to the fixed commits)
- Debian Linux 11.0
- Distributions shipping vulnerable upstream Linux kernel builds
Discovery Timeline
- 2024-07-29 - CVE-2024-41096 published to the National Vulnerability Database (NVD)
- 2025-01 - Debian LTS security announcement released
- 2026-03-24 - Last updated in NVD database
Technical Details for CVE-2024-41096
Vulnerability Analysis
The vulnerability stems from improper lifetime management of an MSI descriptor inside msi_capability_init(). During PCI MSI setup, the kernel allocates a descriptor via msi_alloc_desc() and inserts it through msi_domain_insert_msi_desc(). When __msi_domain_alloc_locked() later fails, msi_domain_free_locked() frees that descriptor. Control then returns to msi_capability_init(), which still holds a stale pointer and dereferences it to perform an unmask operation on the error exit path.
The result is a classic use-after-free read against an object from the kmalloc-128 slab cache. KFENCE captured the allocation in msi_setup_msi_desc() and the subsequent free in msi_domain_free_descs(), confirming the dangling reference. An attacker able to influence MSI allocation failures, for example by exhausting interrupt resources or racing device probe paths, can cause the kernel to operate on freed memory.
Root Cause
The defect is an ownership and lifetime mismatch. msi_capability_init() retained a pointer to a descriptor whose freeing is handled by the deeper msi_domain_alloc_irqs_all_locked() failure path. The function did not re-fetch or copy the descriptor before using it on the error exit, violating the invariant that callers must not dereference descriptors after a failure propagates from the domain allocator.
Attack Vector
Exploitation requires local access with the ability to trigger PCI MSI initialization, typically through device drivers, hotplug events, or interfaces that invoke pci_alloc_irq_vectors(). The attack vector is local with low privileges and no user interaction, but successful exploitation grants kernel-level impact across confidentiality, integrity, and availability.
The upstream fix copies the descriptor before the operations that may free the original, so the error exit path operates on the local copy. The corrective commits are tracked under 0ae40b2d, 45fc8d20, 9eee5330, and ff1121d2 in the stable kernel tree.
Detection Methods for CVE-2024-41096
Indicators of Compromise
- KFENCE or KASAN kernel log entries reporting use-after-free read in __pci_enable_msi_range
- Unexpected kernel oops or panic messages referencing msi_capability_init, msi_domain_free_descs, or pci_alloc_irq_vectors_affinity
- Slab corruption warnings in dmesg related to the kmalloc-128 cache during PCI device initialization
Detection Strategies
- Inventory running kernel versions across Linux fleets and compare against the fixed stable commits referenced in the upstream advisories
- Monitor dmesg and /var/log/kern.log for MSI allocation failures followed by oops traces involving the PCI subsystem
- Enable KFENCE on representative test systems to surface latent use-after-free conditions in PCI driver code paths
Monitoring Recommendations
- Forward kernel ring buffer events to a centralized logging or SIEM platform and alert on PCI/MSI error patterns
- Track package versions of linux-image-* on Debian hosts and flag systems still running pre-patch builds
- Audit drivers that frequently call pci_alloc_irq_vectors() for abnormal failure rates that may indicate exploitation attempts
How to Mitigate CVE-2024-41096
Immediate Actions Required
- Apply the latest stable Linux kernel update from your distribution vendor that includes the upstream fix commits
- For Debian 11 systems, install the kernel package update referenced in the Debian LTS Security Announcement
- Reboot affected systems after patch installation to load the corrected kernel image
- Restrict local shell and container escape vectors so that only trusted users can interact with low-level device interfaces
Patch Information
The fix copies the MSI descriptor and uses the copy on the error exit unmask path, eliminating the dangling reference. The corrective changes are present in the upstream stable kernel commits 0ae40b2d, 45fc8d20, 9eee5330, and ff1121d2. Downstream distribution kernels incorporating these commits are not affected.
Workarounds
- Limit local user access on multi-tenant systems until the kernel patch is applied
- Disable or restrict drivers that perform dynamic MSI allocation if they are non-essential to the workload
- Apply standard kernel hardening, including SMEP, SMAP, and KASLR, to raise the cost of exploiting kernel use-after-free conditions
# Example: update and reboot a Debian system to apply the kernel patch
sudo apt update
sudo apt install --only-upgrade linux-image-$(uname -r | sed 's/.*-//')
sudo reboot
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
