{"id":"CVE-2026-64431","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-64431","generatedAt":"2026-10-28T03:29:14.294Z","title":"In the Linux kernel, the following vulnerability has been resolved: ntfs: avoid calling post_write_mst_fixup() for invalid index_block ntfs_icx_ib_sync_write() calls post_write_mst_fixup() when ntfs_ib_write() returns an error, intending to restore the…","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nntfs: avoid calling post_write_mst_fixup() for invalid index_block\n\nntfs_icx_ib_sync_write() calls post_write_mst_fixup() when ntfs_ib_write()\nreturns an error, intending to restore the buffer after a failed write.\n\nHowever, ntfs_ib_write() returns an error immediately if\npre_write_mst_fixup() validation fails. The caller,\nntfs_icx_ib_sync_write(), interprets any error as a write failure\nrequiring rollback. It does not differentiate between I/O errors and\nvalidation failures, and calls post_write_mst_fixup() anyway.\n\nSince post_write_mst_fixup() assumes that the index_block contents is\ncorrect, it doesn't perform the boundary checks, which results in\nout-of-bounds memory access.\n\nAn attacker can craft a malicious NTFS image with:\n  - large index_block.usa_ofs offset, pointing outside the ntfs_record\n  - index_block.usa_count = 0, causing integer underflow\n  - or index_block.usa_count larger than actual number of sectors in the\n    ntfs_record, causing out-of-bounds access\n\nKASAN reports describing the memory corruption:\n  ==================================================================\n  BUG: KASAN: slab-out-of-bounds in post_write_mst_fixup+0x19c/0x1d0\n  Read of size 2 at addr ffff8881586c9018 by task p/9428\n  Call Trace:\n   <TASK>\n   dump_stack_lvl+0x100/0x190\n   print_report+0x139/0x4ad\n   ? post_write_mst_fixup+0x19c/0x1d0\n   ? __virt_addr_valid+0x262/0x500\n   ? post_write_mst_fixup+0x19c/0x1d0\n   kasan_report+0xe4/0x1d0\n   ? post_write_mst_fixup+0x19c/0x1d0\n   post_write_mst_fixup+0x19c/0x1d0\n   ntfs_icx_ib_sync_write+0x179/0x220\n   ntfs_inode_sync_filename+0x83d/0x1080\n   __ntfs_write_inode+0x1049/0x1480\n   ntfs_file_fsync+0x131/0x9b0\n  ==================================================================\n  BUG: KASAN: slab-out-of-bounds in post_write_mst_fixup+0x1aa/0x1d0\n  Write of size 2 at addr ffff8881586c91fe by task p/9428\n  Call Trace:\n   <TASK>\n   dump_stack_lvl+0x100/0x190\n   print_report+0x139/0x4ad\n   ? post_write_mst_fixup+0x1aa/0x1d0\n   ? __virt_addr_valid+0x262/0x500\n   ? post_write_mst_fixup+0x1aa/0x1d0\n   kasan_report+0xe4/0x1d0\n   ? post_write_mst_fixup+0x1aa/0x1d0\n   post_write_mst_fixup+0x1aa/0x1d0\n   ntfs_icx_ib_sync_write+0x179/0x220\n   ntfs_inode_sync_filename+0x83d/0x1080\n   __ntfs_write_inode+0x1049/0x1480\n   ntfs_file_fsync+0x131/0x9b0\n  ==================================================================\n\nLet's move the post_write_mst_fixup() call to ntfs_ib_write().\nThe ntfs_ib_write() function calls pre_write_mst_fixup() at the beginning.\nIf the index_block contents is invalid, pre_write_mst_fixup() fails and\nntfs_ib_write() returns early without calling post_write_mst_fixup() on\nbad index_block.","published":"2026-07-25T10:17:27.000Z","lastModified":"2026-09-03T18:29:10.000Z","status":"Analyzed","sourceIdentifier":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","cvss":{"version":"3.1","score":7.8,"severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"},"cwe":["CWE-787"],"affected":["linux/linux kernel"],"epss":{"score":0.00165,"percentile":0.05683,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.17%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://git.kernel.org/stable/c/5b6eedd7cc2936f9238e852b553a1b326105bde8","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/e2018628301a6d9f54e34b0cb417f1688c66df1d","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-64431","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}