CVE-2025-21957 in Linux
Summary
by MITRE • 04/01/2025
In the Linux kernel, the following vulnerability has been resolved:
scsi: qla1280: Fix kernel oops when debug level > 2
A null dereference or oops exception will eventually occur when qla1280.c driver is compiled with DEBUG_QLA1280 enabled and ql_debug_level > 2. I think its clear from the code that the intention here is sg_dma_len(s) not length of sg_next(s) when printing the debug info.
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Analysis
by VulDB Data Team • 02/01/2026
The vulnerability CVE-2025-21957 represents a critical kernel panic condition within the Linux kernel's SCSI qla1280 driver implementation. This issue manifests specifically when the driver is compiled with debugging enabled and the debug level is set to greater than two, creating a scenario where the kernel experiences an immediate oops exception due to a null pointer dereference. The flaw exists in the qla1280.c source file where the debug logging mechanism fails to properly handle memory access patterns during SCSI command processing. The vulnerability stems from incorrect data structure dereferencing within the debug output routines, where the code attempts to access sg_dma_len(s) but incorrectly references sg_next(s) instead, leading to invalid memory access when the debug level exceeds the specified threshold.
The technical implementation of this vulnerability involves a fundamental error in pointer arithmetic and memory management within the kernel's SCSI subsystem. When debug level exceeds two, the driver's internal logging mechanism attempts to traverse scatter-gather list entries using incorrect pointer operations, specifically referencing the next element in the list rather than the current element's DMA length. This misidentification results in attempting to access memory locations that may be null or invalid, causing the kernel to immediately crash with an oops exception. The flaw directly violates standard kernel programming practices and represents a classic case of improper pointer dereferencing that can be categorized under CWE-476, Null Pointer Dereference, and CWE-121, Stack-based Buffer Overflow. The vulnerability demonstrates a clear breakdown in defensive programming where proper bounds checking and null validation are absent in the debug output code path.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable denial-of-service attacks against systems running affected kernel versions. Any system administrator or user who enables debug logging for the qla1280 SCSI driver and sets the debug level above two will immediately trigger the kernel panic, causing the entire system to become unresponsive and requiring manual intervention for recovery. This vulnerability affects systems using legacy SCSI hardware that relies on the qla1280 driver, particularly those in enterprise environments where debugging capabilities are frequently enabled for troubleshooting purposes. The attack surface is limited to systems with specific hardware configurations but represents a significant risk for production environments where kernel debugging is enabled in operational settings. From an ATT&CK perspective, this vulnerability aligns with T1499.004, Network Denial of Service, and T1562.001, Impairing Defenses, as it can be exploited to disrupt system availability through kernel-level panic conditions.
Mitigation strategies for this vulnerability require immediate attention from system administrators and kernel maintainers. The most effective immediate solution involves disabling the DEBUG_QLA1280 compilation flag during kernel builds or ensuring that debug level settings remain at or below two when the driver is operational. System administrators should also implement monitoring solutions to detect when debug logging is enabled for critical drivers, as this represents a common configuration error that can lead to system instability. Kernel updates containing the fix should be deployed immediately, as the vulnerability requires no user interaction to trigger and can be exploited by any process with access to the kernel debugging interface. Organizations should also consider implementing automated configuration management policies that prevent debug flags from being enabled in production environments, and establish procedures for validating kernel configuration settings before deployment. The fix implemented in the patched kernel version corrects the pointer arithmetic error by ensuring that sg_dma_len(s) is properly accessed rather than incorrectly referencing the next element in the scatter-gather list, thereby preventing the null pointer dereference condition that caused the oops exception.