CVE-2026-98726 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
nvme-multipath: fix underflow in ANA log bounds checks
The number of ANA groups advertised through Identify Controller sizes the ANA log buffer. The ANA log header and group descriptors independently supply the number of groups and namespace IDs to parse.
Both bounds checks subtract an untrusted object size from ana_log_size before comparing the current offset. If the object is larger than the buffer, the size_t subtraction underflows and lets the parser read beyond ana_log_buf.
Check the current offset before the first subtraction and compare each object size with the remaining buffer instead. This rejects inconsistent ANA data before dereferencing a truncated group descriptor or walking an oversized namespace ID array.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel's NVMe multipath subsystem contains a critical integer underflow vulnerability within its Asymmetric Namespace Access (ANA) log parsing logic, specifically identified as CVE-2024-something depending on the specific release cycle but technically rooted in improper bounds checking during buffer validation. This flaw arises from the way the parser handles data structures supplied by the NVMe controller hardware or firmware. When a host queries an NVMe device for its ANA state, the controller advertises the number of ANA groups via the Identify Controller command, which dictates the size allocated for the ANA log buffer in memory. However, the actual content of this buffer includes a header and multiple group descriptors that independently specify counts for groups and associated namespace IDs. The vulnerability exists because the existing validation logic performs subtraction operations on untrusted object sizes derived from these device-supplied fields before comparing them against the total available buffer size.
The core technical flaw is an unsigned integer underflow condition inherent to C programming when subtracting a larger value from a smaller one using unsigned types such as size_t. In this specific implementation, the code attempts to verify that there is sufficient space in the ana_log_buf for upcoming data structures by calculating remaining space through subtraction. If the object size described in the device's ANA log header or group descriptors exceeds the allocated buffer size, the subtraction operation wraps around due to unsigned integer arithmetic rules. This underflow results in a massive positive value representing the remaining buffer space, which erroneously passes subsequent bounds checks that compare this result against current offsets. Consequently, the parser proceeds to read and process data structures that extend far beyond the boundaries of the allocated ana_log_buf memory region.
This out-of-bounds read vulnerability allows for potential information disclosure or denial of service conditions depending on how the kernel handles the invalid memory access. An attacker with physical access to an NVMe device capable of manipulating its firmware responses, or a malicious virtualized environment where the guest OS acts as the host and controls the emulated NVMe controller presented by QEMU or similar hypervisors, can craft malformed ANA log data. By providing object sizes larger than the buffer, the attacker triggers the underflow condition. The kernel then dereferences pointers into unmapped memory or reads sensitive kernel stack/heap contents adjacent to the buffer. This could lead to a kernel panic causing a system crash, effectively resulting in a denial of service for all services running on that host. In more complex exploitation scenarios involving specific memory layouts, reading arbitrary kernel memory might leak cryptographic keys or other sensitive data, although the primary impact is typically stability-related due to the read-only nature of this specific parsing path before any write operations occur.
From a classification perspective, this vulnerability aligns with CWE-190 Integer Overflow or Wraparound and CWE-20 Improper Input Validation within the Common Weakness Enumeration framework. It also maps to ATT&CK technique T1537 Deep Packet Inspection if viewed through the lens of network protocol manipulation in virtualized environments, though more accurately it represents a local privilege escalation vector via kernel memory corruption risks associated with improper input validation from hardware interfaces. The vulnerability highlights the dangers of trusting untrusted data structures provided by peripheral devices without rigorous pre-validation of their internal consistency and size constraints relative to allocated buffers.
The resolution involves restructuring the bounds checking logic within the nvme-multipath module to prevent underflow conditions entirely. Instead of subtracting object sizes from the total buffer size, the fix mandates checking if the current offset plus the expected object size exceeds the remaining available space in a manner that avoids subtraction-based validation for untrusted inputs. Specifically, the parser now verifies the current offset against the first boundary condition before performing any arithmetic that could underflow. It also explicitly compares each individual object's declared size with the actual remaining buffer capacity using addition or direct comparison methods that do not rely on unsigned wraparound properties. This approach ensures that inconsistent or oversized ANA data is rejected early in the parsing process, preventing dereferencing of truncated group descriptors and avoiding walks through namespace ID arrays that would exceed memory boundaries.
Mitigation strategies for system administrators involve ensuring that Linux kernels are updated to versions containing this patch immediately. For environments utilizing virtualized NVMe devices, hypervisor vendors should also verify their emulation logic does not inadvertently trigger such conditions by sending malformed ANA logs during initialization or state change events. Additionally, enabling kernel hardening features such as KASAN (Kernel Address Sanitizer) in development and testing environments can help detect similar out-of-bounds access issues before they reach production systems. Organizations relying on NVMe multipathing for high availability should prioritize these updates to maintain system integrity against potential denial of service attacks originating from compromised or malicious storage devices connected via PCIe or other supported interfaces.