CVE-2026-93077 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
cxl/features: Clamp Get Feature output size to the remaining buffer
cxl_get_feature() reads a feature in a loop but passes a fixed size_out as the output capacity every iteration. On the last partial iteration the buffer has less room left, so a device that returns more than asked can overflow feat_out.
Use the per-iter size data_to_rd_size, which already tracks the remaining room, as the output capacity.
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Analysis
by VulDB Data Team • 09/18/2026
The Linux kernel driver for Compute Express Link features contains a critical memory safety vulnerability within the cxl_get_feature function that allows for potential buffer overflows during feature retrieval operations. This issue stems from an improper handling of output buffer sizes when processing data returned by hardware devices. The core technical flaw lies in how the function manages iterative reads from device registers or memory-mapped I/O regions associated with CXL features. Specifically, cxl_get_feature employs a loop structure to read feature data in chunks, yet it consistently passes a fixed size_out parameter representing the total allocated buffer capacity during each iteration rather than calculating the remaining available space within that buffer for subsequent writes.
This architectural oversight creates a dangerous condition where devices capable of returning more data than initially requested can cause an out-of-bounds write operation. On the final partial iteration of the loop, when only a fraction of the original buffer remains unused, passing the full initial size_out value as the output capacity leads to writing beyond the allocated memory boundaries. Such behavior constitutes a classic heap or stack-based buffer overflow depending on where feat_out is located in memory. An attacker with local access who can trigger this code path through specific CXL device interactions may exploit this flaw to corrupt adjacent memory structures, potentially leading to arbitrary code execution, privilege escalation, or system instability and crashes due to segmentation faults or kernel panics.
From a vulnerability classification perspective, this defect aligns closely with CWE-120 Buffer Copy without Checking Size of Input Classic buffer overflow vulnerabilities where the input size is not properly validated against the destination buffer capacity before copying data. Additionally, it relates to CWE-787 Out-of-bounds Write which occurs when software writes data past the end or before the beginning of the intended buffer. In terms of attack vectors and techniques, this vulnerability could be leveraged within the context of ATT&CK technique T1059 Command and Scripting Interpreter if exploited for initial access followed by privilege escalation via local code execution, although it primarily represents a memory corruption issue that facilitates further exploitation stages rather than being an independent lateral movement or persistence mechanism itself.
The operational impact of this vulnerability extends beyond immediate system compromise to include potential denial of service conditions where kernel stability is compromised through memory corruption events. Systems utilizing CXL devices for high-performance computing tasks, such as those involving accelerators like GPUs or FPGAs connected via the Compute Express Link interface, are particularly susceptible if they interact with firmware or hardware features that return variable-length responses exceeding expected limits. The lack of bounds checking during iterative data retrieval means that any malformed or maliciously crafted response from a CXL device can trigger this overflow condition without requiring complex exploitation techniques beyond triggering the specific code path under controlled conditions.
To mitigate this vulnerability, developers must ensure that all buffer write operations strictly adhere to remaining capacity calculations rather than relying on static size parameters throughout iterative processes. The resolution involves modifying cxl_get_feature to utilize per-iteration data tracking mechanisms such as data_to_rd_size which accurately reflects the actual remaining room in the output buffer for each read operation. This adjustment ensures that writes never exceed available memory space regardless of how much data a device attempts to return. Administrators should apply kernel updates containing this patch immediately and verify that all connected CXL devices operate with updated firmware versions that minimize excessive response sizes where possible. Regular auditing of driver code for similar patterns in other iterative read functions is also recommended to prevent analogous vulnerabilities across the broader Linux kernel subsystems managing hardware interfaces.