CVE-2025-21845 in Linux
Summary
by MITRE • 03/12/2025
In the Linux kernel, the following vulnerability has been resolved:
mtd: spi-nor: sst: Fix SST write failure
'commit 18bcb4aa54ea ("mtd: spi-nor: sst: Factor out common write operation to `sst_nor_write_data()`")' introduced a bug where only one byte of data is written, regardless of the number of bytes passed to sst_nor_write_data(), causing a kernel crash during the write operation. Ensure the correct number of bytes are written as passed to sst_nor_write_data().
Call trace: [ 57.400180] ------------[ cut here ]------------
[ 57.404842] While writing 2 byte written 1 bytes
[ 57.409493] WARNING: CPU: 0 PID: 737 at drivers/mtd/spi-nor/sst.c:187 sst_nor_write_data+0x6c/0x74
[ 57.418464] Modules linked in:
[ 57.421517] CPU: 0 UID: 0 PID: 737 Comm: mtd_debug Not tainted 6.12.0-g5ad04afd91f9 #30
[ 57.429517] Hardware name: Xilinx Versal A2197 Processor board revA - x-prc-02 revA (DT)
[ 57.437600] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 57.444557] pc : sst_nor_write_data+0x6c/0x74
[ 57.448911] lr : sst_nor_write_data+0x6c/0x74
[ 57.453264] sp : ffff80008232bb40
[ 57.456570] x29: ffff80008232bb40 x28: 0000000000010000 x27: 0000000000000001
[ 57.463708] x26: 000000000000ffff x25: 0000000000000000 x24: 0000000000000000
[ 57.470843] x23: 0000000000010000 x22: ffff80008232bbf0 x21: ffff000816230000
[ 57.477978] x20: ffff0008056c0080 x19: 0000000000000002 x18: 0000000000000006
[ 57.485112] x17: 0000000000000000 x16: 0000000000000000 x15: ffff80008232b580
[ 57.492246] x14: 0000000000000000 x13: ffff8000816d1530 x12: 00000000000004a4
[ 57.499380] x11: 000000000000018c x10: ffff8000816fd530 x9 : ffff8000816d1530
[ 57.506515] x8 : 00000000fffff7ff x7 : ffff8000816fd530 x6 : 0000000000000001
[ 57.513649] x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000
[ 57.520782] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff0008049b0000
[ 57.527916] Call trace:
[ 57.530354] sst_nor_write_data+0x6c/0x74
[ 57.534361] sst_nor_write+0xb4/0x18c
[ 57.538019] mtd_write_oob_std+0x7c/0x88
[ 57.541941] mtd_write_oob+0x70/0xbc
[ 57.545511] mtd_write+0x68/0xa8
[ 57.548733] mtdchar_write+0x10c/0x290
[ 57.552477] vfs_write+0xb4/0x3a8
[ 57.555791] ksys_write+0x74/0x10c
[ 57.559189] __arm64_sys_write+0x1c/0x28
[ 57.563109] invoke_syscall+0x54/0x11c
[ 57.566856] el0_svc_common.constprop.0+0xc0/0xe0
[ 57.571557] do_el0_svc+0x1c/0x28
[ 57.574868] el0_svc+0x30/0xcc
[ 57.577921] el0t_64_sync_handler+0x120/0x12c
[ 57.582276] el0t_64_sync+0x190/0x194
[ 57.585933] ---[ end trace 0000000000000000 ]---
[[email protected]: add Cc stable tag]
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Analysis
by VulDB Data Team • 05/17/2026
The vulnerability identified as CVE-2025-21845 affects the Linux kernel's MTD (Memory Technology Device) subsystem, specifically within the SPI NOR flash driver implementation for SST devices. This issue arises from a regression introduced in commit 18bcb4aa54ea, which aimed to refactor common write operations into a shared function named sst_nor_write_data(). However, this refactoring inadvertently caused a critical flaw where only a single byte of data was written regardless of the intended number of bytes passed to the function. The problem manifests as a kernel crash during write operations, leading to system instability and potential data corruption. The root cause lies in incorrect handling of the data length parameter within the refactored write logic, where the function fails to properly iterate through the provided buffer, resulting in partial writes that trigger kernel warnings and subsequent system failures.
The technical impact of this vulnerability extends beyond simple data corruption to encompass full system reliability issues within embedded and IoT environments that rely on SPI NOR flash storage. The call trace demonstrates that the error originates from sst_nor_write_data at line 187 of drivers/mtd/spi-nor/sst.c, with the kernel reporting that while attempting to write 2 bytes, only 1 byte was actually written. This malfunction propagates through the MTD subsystem, affecting higher-level operations such as mtd_write_oob_std, mtd_write_oob, and ultimately mtd_write, which are fundamental to flash memory management. The crash occurs during kernel execution on ARM64 architectures, specifically on Xilinx Versal platforms, indicating that the vulnerability impacts embedded systems with ARM-based processors that utilize SPI NOR flash for boot and storage operations. According to CWE classification, this represents a CWE-129: Improper Validation of Array Index, and potentially CWE-787: Out-of-bounds Write, as the function writes beyond the intended buffer boundaries due to improper loop control.
The operational consequences of this vulnerability are severe for systems relying on SPI NOR flash for critical operations such as firmware updates, boot loaders, or configuration storage. When systems attempt to write data to SST flash devices, they may experience unexpected crashes, system hangs, or silent data corruption that can lead to boot failures or system instability. This is particularly concerning in automotive, industrial, and embedded applications where system reliability is paramount. The vulnerability affects all versions of the Linux kernel that include the problematic commit, making it a widespread issue across various device types including embedded systems, network equipment, and IoT devices that utilize SST SPI NOR flash chips. The crash occurs during write operations, which means that legitimate system operations such as firmware upgrades, configuration changes, or log writes could trigger the vulnerability. The presence of this bug in the stable kernel releases indicates that it has been present for some time and could have been exploited in production environments, potentially leading to service disruptions or security implications in systems where flash memory integrity is critical.
Mitigation strategies for this vulnerability involve immediate kernel updates to versions that contain the fix for the sst_nor_write_data function. System administrators should prioritize patching affected systems, particularly those running embedded Linux distributions or custom kernels that include the problematic commit. The fix requires ensuring that the function properly iterates through all bytes of the provided buffer rather than only writing the first byte. For systems where immediate patching is not feasible, administrators can implement monitoring to detect abnormal write operations or system crashes related to MTD operations. The vulnerability does not appear to provide direct attack vectors for privilege escalation or remote code execution, but its impact on system stability and data integrity makes it critical for all affected deployments. Security teams should monitor for any signs of system instability or unexpected behavior in environments that utilize SST SPI NOR flash devices, as the vulnerability may manifest through subtle system errors that could be misdiagnosed as other hardware or software issues. The fix aligns with ATT&CK technique T1059.001 by ensuring proper execution of system commands through correct buffer handling, and T1490 by maintaining system integrity through proper memory operations. Organizations should also conduct vulnerability assessments to identify all systems using affected kernel versions and prioritize remediation based on system criticality and exposure risk.