CVE-2026-80959 in Linux
Summary
by MITRE • 09/11/2026
In the Linux kernel, the following vulnerability has been resolved:
dm-pcache: bound the persisted tail-position offset
cache_pos_decode() takes the persisted key_tail and dirty_tail seg_off from the cache device and addresses within the segment with it. A seg_off at or past the segment data_size, controllable by whoever supplies the device (CAP_SYS_ADMIN), reads past the segment data.
Reject a decoded seg_off that is not below the segment data_size.
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Analysis
by VulDB Data Team • 09/12/2026
The Linux kernel's device-mapper persistent cache implementation contains an out-of-bounds read vulnerability within the dm-pcache subsystem, specifically in the function responsible for decoding cache positions. This flaw arises from insufficient validation of metadata retrieved during the initialization or recovery phase of a cached block device. When the system reconstructs its internal state by reading persisted keys and dirty tails from the storage medium, it extracts segment offsets that dictate where data resides within memory segments. The code currently fails to verify whether these extracted offset values are strictly less than the defined size of the target segment's data area. Consequently, if a crafted or corrupted metadata structure is present on disk, the kernel will attempt to access memory locations beyond the allocated boundaries of the segment buffer.
This vulnerability allows for an out-of-bounds read operation that can potentially expose sensitive kernel memory contents to user space processes with appropriate privileges. Since the persistence layer relies on data written by privileged users or system administrators during normal operations, an attacker with CAP_SYS_ADMIN capabilities could manipulate the underlying storage metadata to embed malicious offset values. Upon subsequent mounting or activation of the device-mapper target, the kernel would process these invalid offsets without raising a bounds check error. The resulting memory access violation may lead to information disclosure, where internal kernel structures such as pointers, cryptographic keys, or other sensitive data are leaked through side channels or direct read operations if exposed via sysfs or debug interfaces. In more severe scenarios involving subsequent write operations based on corrupted state derived from this initial read, the integrity of the cached data could be compromised, potentially leading to denial of service conditions due to kernel panics triggered by invalid memory accesses.
From a classification perspective, this issue aligns with CWE-125, which describes an out-of-bounds read vulnerability where software reads past the end of a buffer or array. The attack vector is primarily local and requires high privilege levels initially to manipulate the persistent storage metadata, placing it within the context of CWE-780, which covers improper validation of insufficiently trusted inputs in persistence mechanisms. In terms of adversarial tactics as defined by MITRE ATT&CK, this vulnerability facilitates initial access or defense evasion through data manipulation on disk-based artifacts that are later processed with elevated privileges. It represents a classic case where trust assumptions regarding the integrity of persisted state information lead to unsafe memory operations when those assumptions are violated by maliciously crafted inputs.
The resolution involves implementing strict boundary checks within the cache position decoding logic. Specifically, the validation routine must ensure that any decoded segment offset is strictly less than the configured data size for the corresponding segment before it is used for memory addressing. This defensive programming practice ensures that even if corrupted or adversarial metadata is present on disk, the kernel will reject invalid configurations rather than attempting to access out-of-bounds memory regions. System administrators should apply the relevant kernel update as soon as possible to mitigate this risk. Additionally, organizations relying on device-mapper persistent caching for critical workloads should audit their storage infrastructure for signs of tampering or corruption in metadata sectors, although the primary mitigation remains patching the underlying kernel code to enforce rigorous input validation during state reconstruction phases.