CVE-2026-74470 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
scsi: scsi_debug: Fix REPORT ZONES alloc_len underflow OOB write
resp_report_zones() sizes the reply buffer from the CDB allocation length. The v3 fix rounds alloc_len up with ALIGN() before deriving the descriptor count:
rep_max_zones = (ALIGN((u64)alloc_len, RZONES_DESC_HD) - RZONES_DESC_HD) >> ilog2(RZONES_DESC_HD); arr_len = (u64)RZONES_DESC_HD * (rep_max_zones + 1);
For alloc_len in 0xFFFFFFC1..0xFFFFFFFF, ALIGN() rounds up to 0x100000000, so arr_len is 4 GB. On 32-bit, kzalloc()'s size_t is 32-bit and truncates 0x100000000 to 0; kzalloc(0) returns ZERO_SIZE_PTR, which passes the !arr check, and desc = arr + 64 is then dereferenced in the loop -> out-of-bounds write / panic.
Clamp rep_max_zones to devip->nr_zones. The loop already stops at sdebug_capacity (after nr_zones zones), so a report can never hold more than nr_zones descriptors; the clamp does not change the report, it only bounds arr_len to (nr_zones + 1) * RZONES_DESC_HD, a real device property that can never reach 0x100000000.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability identified in the Linux kernel's SCSI subsystem affects the scsi_debug driver component, specifically within the resp_report_zones() function that handles REPORT ZONES commands. This issue represents a critical memory safety flaw that could potentially lead to system instability or exploitation. The vulnerability stems from improper handling of buffer allocation lengths during zone report generation, creating conditions for out-of-bounds memory writes that can result in kernel panics or arbitrary code execution.
The technical flaw manifests when processing the CDB allocation length parameter in the REPORT ZONES command implementation. The original code calculates the reply buffer size based directly on the allocation length value without proper validation of boundary conditions. When allocation lengths fall within the range of 0xFFFFFFC1 to 0xFFFFFFFF, the ALIGN() function rounds up to 0x100000000, resulting in an extremely large buffer calculation that exceeds typical memory constraints. This particular mathematical overflow condition creates a scenario where memory allocation functions on 32-bit systems receive values that exceed their 32-bit size_t limits, causing truncation to zero and subsequent dereference of invalid memory locations.
The operational impact of this vulnerability is significant in environments running 32-bit Linux kernels with SCSI debugging enabled. The out-of-bounds write condition occurs when the code attempts to calculate descriptor counts and subsequently dereferences memory at an offset that extends far beyond the allocated buffer boundaries. This creates a potential for kernel panic conditions or more severe exploitation scenarios where malicious actors could leverage this flaw to execute arbitrary code within kernel space. The vulnerability specifically affects systems where scsi_debug is active, which typically occurs in testing environments or specialized storage configurations.
The fix implemented addresses multiple aspects of the vulnerability by introducing proper bounds checking and clamping mechanisms. The solution modifies the calculation logic to clamp the rep_max_zones value to the device's actual zone count, ensuring that buffer allocations remain within reasonable limits based on real device properties rather than potentially malicious input values. This approach prevents the excessive memory allocation that could occur with large allocation length values while maintaining functional correctness for legitimate use cases. The fix aligns with established security practices for preventing integer overflows and buffer overruns, similar to common mitigations recommended under CWE-129 and CWE-787 categories. Additionally, this vulnerability demonstrates characteristics relevant to ATT&CK technique T1068 which involves exploiting local privilege escalation opportunities through kernel vulnerabilities, making proper mitigation essential for maintaining system integrity.
The resolution effectively prevents the integer overflow condition by ensuring that buffer sizes are always bounded by the actual device zone count rather than allowing arbitrary large values derived from potentially malicious input. This approach maintains the functional requirements of the SCSI debugging interface while eliminating the memory safety issues that could be exploited in kernel space. The implementation follows standard security principles for preventing out-of-bounds memory access patterns and aligns with industry best practices for kernel memory management and input validation, ensuring robust protection against similar vulnerabilities in related subsystems.