CVE-2026-68293 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
net/mlx5: Fix MCIA register buffer overflow on 32 dword reads
The MCIA register can return up to 32 dwords (128 bytes) when the device advertises the mcia_32dwords capability, but struct mlx5_ifc_mcia_reg_bits only defines dword_0..11, leaving room for just 12 dwords (48 bytes) of data.
mlx5_query_mcia() clamps the read size to mlx5_mcia_max_bytes() and then memcpy()s that many bytes out of the register, potentially reading past the end of the 'out' buffer. On kernels built with FORTIFY_SOURCE this is caught as a buffer overflow while reading the module EEPROM via ethtool:
detected buffer overflow in memcpy kernel BUG at lib/string_helpers.c:1048! RIP: 0010:fortify_panic+0x13/0x20 Call Trace: mlx5_query_mcia.isra.0+0x200/0x210 [mlx5_core]
mlx5_query_module_eeprom_by_page+0x4a/0xa0 [mlx5_core]
mlx5e_get_module_eeprom_by_page+0xbb/0x120 [mlx5_core]
eeprom_prepare_data+0xf3/0x170 ethnl_default_doit+0xf1/0x3b0
Extend the mcia_reg layout to 32 dwords.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability resides in the mlx5 network driver within the Linux kernel, specifically affecting the MCIA (Management Controller Interface Access) register handling mechanism. This issue manifests when devices advertise the mcia_32dwords capability, which allows the MCIA register to return up to 32 dwords of data totaling 128 bytes. The underlying problem stems from a fundamental mismatch between the advertised capability and the defined data structure within the kernel codebase.
The technical flaw occurs in the mlx5_query_mcia() function where the system attempts to read data from the MCIA register using a buffer that is insufficiently sized for the maximum possible data return. While the function correctly clamps the read size to mlx5_mcia_max_bytes(), which should theoretically prevent overflows, the memcpy() operation still operates on a structure definition that only accounts for 12 dwords or 48 bytes of data. This structural inconsistency creates a scenario where the system attempts to copy more data than the allocated buffer can accommodate.
The operational impact of this vulnerability becomes particularly severe when the kernel is compiled with FORTIFY_SOURCE enabled, which adds additional runtime checks for buffer overflows. During normal operation, when attempting to read module EEPROM information via ethtool commands, the system triggers a buffer overflow condition that results in a kernel panic and system crash. The stack trace reveals the exact point of failure occurring in fortify_panic function within lib/string_helpers.c, indicating that the memory corruption has been detected and handled as a critical error condition.
This vulnerability directly relates to CWE-121, which describes stack-based buffer overflow conditions, and more specifically maps to CWE-787, representing out-of-bounds write operations. The attack surface is primarily through network device management interfaces and module EEPROM access operations, making it particularly concerning for enterprise networking environments where mlx5-based adapters are commonly deployed. The ATT&CK framework categorizes this under privilege escalation and defense evasion techniques, as successful exploitation could lead to system instability or potential privilege escalation.
The fix implemented involves extending the mcia_reg layout definition from 12 dwords to the full 32 dwords that the hardware capability supports. This change ensures proper alignment between the hardware advertisement and the software implementation, eliminating the buffer overflow condition. The solution directly addresses the root cause by providing adequate memory allocation for the maximum possible data return, thereby preventing any potential out-of-bounds memory access during the MCIA register read operations.
The mitigation strategy requires updating to kernel versions that include this specific fix, as well as ensuring proper system monitoring for buffer overflow conditions during EEPROM access operations. Network administrators should particularly focus on systems running with FORTIFY_SOURCE enabled, as these configurations make such vulnerabilities more apparent and potentially exploitable. Regular kernel updates remain critical for maintaining security posture, especially in environments where network device management through ethtool or similar interfaces is commonly performed.