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CVE-2026-28825 is an out-of-bounds write vulnerability in Apple’s SMB client kernel component, smbfs.kext, affecting macOS prior to macOS Sequoia 15.7.5, macOS Sonoma 14.8.5, and macOS Tahoe 26.4. The flaw is in the SMB 3.1.1 compression handling path, specifically the chained compression transform parsing performed by the function smb2_rq_decompress_read. The vulnerable code allocates a scratch buffer sized at twice OriginalCompressedSegmentSize, using one half for compressed input and the other half for decompressed output. Although the implementation validates that the attacker-controlled OriginalPayloadSize fits within the output half, it fails to verify that the compressed chunk length also fits within the input half before copying data. As a result, attacker-controlled compressed data can overflow the heap buffer during processing of a crafted SMB READ response. Apple addressed the issue by adding improved bounds checking to ensure the compressed length does not exceed OriginalCompressedSegmentSize before the copy occurs. Apple’s advisory describes the security impact as allowing an app to modify protected parts of the file system.
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A kernel heap out-of-bounds write in Apple's smbfs.kext SMB client parsing logic, specifically in smb2_rq_decompress_read handling SMB 3.1.1 chained compression data. A malicious SMB server can supply attacker-controlled length fields that cause oversized copies into a small kernel allocation, leading to kernel panic and likely broader exploitation potential.
An out-of-bounds write vulnerability in macOS Sequoia that could allow an app to modify protected parts of the file system.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.