CVE-2026-98205 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
Input: evdev - zero absinfo before partial copy in EVIOCSABS
The EVIOCSABS handler copies at most the user supplied ioctl size into an uninitialized on-stack struct input_absinfo:
if (copy_from_user(&abs, p, min_t(size_t, size, sizeof(struct input_absinfo))))
The size comes from _IOC_SIZE() of the ioctl command and is therefore fully controlled by userspace. A short size leaves the trailing part of the structure holding whatever was on the kernel stack, and the whole structure is then stored into the device:
dev->absinfo[t] = abs;
EVIOCGABS hands that back to userspace, disclosing the stale stack bytes. Only the resolution field is currently cleared, which covers the legacy struct layout but not an arbitrarily short size.
Zero the structure before the copy so any part not supplied by the caller reads back as zero. The existing resolution fixup is kept, since it also handles a size that partially overlaps that field.
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Analysis
by VulDB Data Team • 10/06/2026
The Linux kernel input subsystem contains a critical information disclosure vulnerability within the EVIOCSABS ioctl handler, which allows local users to read uninitialized kernel stack memory through subsequent queries of absolute axis properties. This flaw stems from an improper handling of variable-length data structures during device configuration updates. Specifically, when a user-space application invokes the EVIOCSABS command to set parameters for an input device's absolute axes, the kernel attempts to copy data from user space into a local struct input_absinfo allocated on the kernel stack. The size of this copy is determined by the _IOC_SIZE macro extracted from the ioctl command argument provided by the caller, meaning the length is entirely under the control of unprivileged userspace processes.
The technical root cause lies in the use of min_t to limit the copy operation to either the user-supplied size or the full sizeof(struct input_absinfo). If a malicious actor supplies an ioctl request with a size smaller than the total structure size, only the initial portion of the stack-allocated buffer is overwritten with valid data. The remaining bytes at the end of the struct retain their previous values from whatever data previously existed on that specific location in the kernel stack. Because the entire struct, including these uninitialized trailing fields, is subsequently assigned to the device's absinfo array via dev->absinfo[t] = abs, the stale memory contents become part of the persistent state for that input axis configuration.
This vulnerability enables a local privilege escalation vector primarily through information disclosure rather than direct code execution or denial of service. An attacker can exploit this by first sending a truncated EVIOCSABS ioctl to populate the device's absolute info structure with partial data and residual stack garbage. Subsequently, the attacker issues an EVIOCGABS ioctl request to retrieve the current configuration for that axis. The kernel returns the full struct input_absinfo, including the uninitialized portion containing sensitive kernel memory contents such as pointers, cryptographic keys, or other process-specific data from prior function calls on the same stack frame. This constitutes a classic out-of-bounds read scenario where the boundary check is applied to the source copy but not to the destination structure's integrity before use in subsequent reads.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-94 Information Exposure Through Kernel Memory Leak. In terms of offensive security frameworks like MITRE ATT&CK, it falls under T1083 File and Directory Discovery or more accurately T1567 Exfiltration Over Alternative Protocol if used in conjunction with other techniques to exfiltrate the leaked data, though primarily it is categorized as Local Privilege Escalation via Information Disclosure. The impact ranges from minor information leakage of non-sensitive stack noise to severe exposure of kernel pointers that can aid in bypassing Kernel Address Space Layout Randomization (KASLR), thereby facilitating further exploitation steps such as arbitrary code execution through return-oriented programming or direct pointer dereference attacks.
The remediation strategy implemented involves zero-initializing the struct input_absinfo before performing the copy_from_user operation. By ensuring that all bytes of the structure are set to zero prior to receiving user data, any portion not explicitly overwritten by the caller will remain null rather than containing stale stack artifacts. This approach guarantees that partial copies result in well-defined structures with zeros for unspecified fields, effectively neutralizing the information leak vector. The existing logic that specifically zeroes out the resolution field is retained as a defensive measure to handle legacy struct layouts and cases where the user-supplied size partially overlaps critical fields, ensuring backward compatibility while closing the broader security gap associated with arbitrary short sizes.