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CVE-2025-39817 is an out-of-bounds read vulnerability in the Linux kernel's EFI variable filesystem (efivarfs), specifically efivarfs_d_compare(). When a directory entry's name length is less than EFI_VARIABLE_GUID_LEN, the computed guid offset can become negative, causing memcmp() to read outside the allocated slab object. Parallel lookups using an invalid filename can expose the condition: one thread adds an invalid directory entry to the hash list, while another retrieves it and invokes the vulnerable comparison. The issue was observed on kernel 6.6 and was also present on the master branch at the time of reporting. It can potentially cause kernel memory disclosure or a kernel crash.
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A slab out-of-bounds read in the Linux kernel's efivarfs_d_compare function, triggered by parallel lookups involving invalid filenames. An insufficient filename-length check allows a negative GUID offset during comparison. The listed CVSS v3 score is 7.1, indicating local exploitation requiring low privileges, with high confidentiality and availability impact and no integrity impact. The fix checks the GUID offset before comparison.
A Linux kernel efivarfs slab out-of-bounds vulnerability in efivarfs_d_compare.
Referenced by the TuxCare CentOS 8.5 security advisory; no vulnerability details are provided.
A Linux kernel efivarfs slab out-of-bounds vulnerability in efivarfs_d_compare.
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Every observed campaign linking this CVE to a named adversary.
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Cross-references every affected SKU, including bundled OEM variants.
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