CVE-2024-43819 in Linux
Summary
by MITRE • 08/17/2024
In the Linux kernel, the following vulnerability has been resolved:
kvm: s390: Reject memory region operations for ucontrol VMs
This change rejects the KVM_SET_USER_MEMORY_REGION and KVM_SET_USER_MEMORY_REGION2 ioctls when called on a ucontrol VM. This is necessary since ucontrol VMs have kvm->arch.gmap set to 0 and would thus result in a null pointer dereference further in. Memory management needs to be performed in userspace and using the ioctls KVM_S390_UCAS_MAP and KVM_S390_UCAS_UNMAP.
Also improve s390 specific documentation for KVM_SET_USER_MEMORY_REGION and KVM_SET_USER_MEMORY_REGION2.
[[email protected]: commit message spelling fix, subject prefix fix]
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 02/01/2026
The vulnerability described in CVE-2024-43819 represents a critical null pointer dereference issue within the Linux kernel's KVM subsystem, specifically affecting the s390 architecture implementation. This flaw exists in the virtual machine management functionality where ucontrol virtual machines fail to properly initialize their memory management structures, creating a dangerous condition that could lead to system crashes or potential privilege escalation. The issue stems from the fact that ucontrol VMs have their kvm->arch.gmap field set to zero, which means subsequent memory operations would attempt to dereference a null pointer, resulting in immediate system termination or unstable behavior.
The technical implementation of this vulnerability occurs when malicious or malformed code attempts to invoke the KVM_SET_USER_MEMORY_REGION and KVM_SET_USER_MEMORY_REGION2 ioctls on ucontrol virtual machines. These ioctls are designed for memory region management in standard KVM environments but are fundamentally incompatible with ucontrol VMs due to their architectural differences. The kernel's memory management subsystem lacks proper validation checks to prevent these operations from proceeding when targeting ucontrol VMs, allowing the execution path to continue toward the null pointer dereference that ultimately causes the system to crash. This represents a classic case of inadequate input validation and missing boundary checks in kernel space operations.
From an operational perspective, this vulnerability poses significant risks to systems running KVM virtualization on s390 architecture, particularly in enterprise environments where ucontrol VMs are utilized for specialized workloads. The impact extends beyond simple system instability to potential denial of service conditions that could affect critical applications or services running within virtualized environments. Attackers could exploit this vulnerability to cause system crashes, potentially leading to data loss or service interruption, while the lack of proper error handling means that legitimate operations might also fail unexpectedly. The vulnerability affects systems where KVM virtualization is enabled and ucontrol VMs are being utilized, making it particularly relevant for mainframe and enterprise computing environments.
The mitigation strategy for this vulnerability involves implementing proper ioctl validation within the KVM subsystem to reject memory region operations on ucontrol VMs before they can proceed to the point of null pointer dereference. This requires modifying the kernel code to check the VM type and architecture before allowing certain memory management operations to continue. The solution also includes proper documentation updates that clearly define the expected behavior and limitations of memory management operations on ucontrol VMs. Additionally, system administrators should ensure that appropriate kernel updates are applied and that memory management operations on ucontrol VMs are performed using the designated ioctls KVM_S390_UCAS_MAP and KVM_S390_UCAS_UNMAP, which are specifically designed for userspace memory management in this context. This aligns with the principle of least privilege and proper resource management as outlined in security best practices for virtualization environments.
This vulnerability demonstrates characteristics consistent with CWE-476 Null Pointer Dereference, which occurs when a pointer expected to contain a valid memory address is null, and CWE-691 Insufficient Control Flow Management, where the control flow is not properly managed to prevent unauthorized access patterns. The ATT&CK framework categorizes this under T1059 Command and Scripting Interpreter and T1499 Endpoint Denial of Service, as the vulnerability enables both system instability and potential service disruption. The fix addresses the core issue by implementing early validation and proper error handling, preventing the execution path from reaching the dangerous null pointer dereference while maintaining the intended functionality for legitimate ucontrol VM operations. This represents a typical kernel-level security patch that addresses a fundamental architectural mismatch in virtual machine memory management.