CVE-2026-64291 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
iommufd: Set veventq_depth upper bound
iommufd_veventq_alloc() accepts any !0 veventq_depth from userspace, with an upper bound at U32_MAX.
This leaves a vulnerability where userspace can allocate excessively large queues to exhaust kernel memory reserves.
Cap the veventq_depth (maximum number of entries) to 1 << 19, matching the maximum number of entries in the SMMUv3 EVTQ (the largest use case today).
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability identified in the Linux kernel relates to improper input validation within the iommufd subsystem, specifically affecting the iommufd_veventq_alloc() function. This function processes veventq_depth parameters provided by userspace without adequate bounds checking, creating a potential denial of service condition through excessive memory allocation. The flaw stems from the absence of a reasonable upper limit on the maximum number of entries that can be specified for virtual event queues, allowing malicious or malformed input to trigger unintended resource consumption patterns.
The technical implementation of this vulnerability occurs when userspace applications pass arbitrary values greater than zero to the veventq_depth parameter, with the kernel accepting any value up to the maximum 32-bit unsigned integer limit. This design flaw enables attackers to specify extremely large queue sizes that can overwhelm kernel memory management systems. The absence of proper validation means that legitimate hardware constraints are not enforced, creating opportunities for memory exhaustion attacks that could compromise system stability and availability.
From an operational perspective, this vulnerability represents a critical security risk that could be exploited to perform resource exhaustion attacks against systems running affected Linux kernels. When attackers specify excessively large veventq_depth values, the kernel attempts to allocate corresponding memory structures that can quickly deplete available system resources. This type of denial of service condition directly impacts system availability and can potentially affect other critical services running on the same platform, making it particularly dangerous in production environments where system reliability is paramount.
The vulnerability aligns with CWE-129, which addresses improper validation of input ranges, and represents a classic example of inadequate bounds checking in kernel space code. The fix implemented by capping veventq_depth to 1 << 19 entries directly addresses the root cause by establishing a reasonable upper limit that matches the maximum number of entries supported by SMMUv3 EVTQ implementations. This approach follows security best practices by implementing defense-in-depth measures that prevent resource exhaustion while maintaining compatibility with existing hardware capabilities.
The mitigation strategy employed in this fix demonstrates proper input validation techniques that align with established security frameworks and industry standards for kernel development. By setting a maximum limit of 524,288 entries (1 << 19) rather than allowing arbitrary values up to U32_MAX, the implementation prevents attackers from exploiting memory allocation patterns to cause system instability. This solution also incorporates elements consistent with ATT&CK framework's resource exhaustion techniques, as it directly addresses the attack surface that could be leveraged for denial of service attacks targeting kernel memory management subsystems.
The specific limit of 1 << 19 entries chosen for this fix is significant because it matches the maximum number of entries in SMMUv3 EVTQ implementations, ensuring that legitimate use cases continue to function while preventing the exploitation of excessive allocation patterns. This approach maintains backward compatibility with existing hardware implementations while establishing robust protection against malicious input. The fix represents a targeted solution that addresses the vulnerability without introducing unnecessary restrictions on legitimate system operations, demonstrating sound security engineering principles in kernel space development and memory management.