{"id":"CVE-2026-63808","summary":"exfat: fix potential use-after-free in exfat_find_dir_entry()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nexfat: fix potential use-after-free in exfat_find_dir_entry()\n\nIn exfat_find_dir_entry(), the buffer_head obtained from\nexfat_get_dentry() is released with brelse(bh) before the fall-through\nTYPE_EXTEND branch reads the directory entry through ep (which points\ninto bh-\u003eb_data):\n\n\tbrelse(bh);\n\tif (entry_type == TYPE_EXTEND) {\n\t\t...\n\t\tlen = exfat_extract_uni_name(ep, entry_uniname);\n\t\t...\n\t}\n\nAfter brelse() drops our reference, nothing guarantees that the\nunderlying page backing bh-\u003eb_data remains valid for the subsequent\nexfat_extract_uni_name() read. This is the same pattern fixed in\ncommit fc961522ddbd (\"exfat: Fix potential use after free in\nexfat_load_upcase_table()\").\n\nMove brelse(bh) so it runs after ep is no longer dereferenced on\neach branch.\n\nConfirmed on QEMU x86_64 with CONFIG_KASAN=y + CONFIG_DEBUG_PAGEALLOC=y\n+ CONFIG_PAGE_POISONING=y on linux-next, using a crafted exFAT image\n(long filename with same-hash collisions forcing the TYPE_EXTEND path).\nWith a debug-only invalidate_bdev() inserted between brelse(bh) and\nthe ep read to make the stale-deref window deterministic, the\nunpatched kernel faults:\n\n  BUG: KASAN: use-after-free in exfat_find_dir_entry+0x133b/0x15a0\n  BUG: unable to handle page fault for address: ffff88801a5fa0c2\n  Oops: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI\n  RIP: 0010:exfat_find_dir_entry+0x1188/0x15a0\n\nWith this patch applied, the same instrumented harness completes\ncleanly under the same sanitizer stack. I have not reproduced a\ncrash on an uninstrumented kernel under ordinary reclaim; the\ninstrumented A/B establishes the lifetime violation and that the\npatch closes it, not an unaided triggerability claim.","modified":"2026-07-23T09:59:47.158374708Z","published":"2026-07-19T12:02:11.323Z","related":["openSUSE-SU-2026:11339-1"],"database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63808.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/06c4e1e9967d332ac33ba38b7819851089ff9359"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3f5f8ee9917cc2b9076ac533492d8a200edcabb8"},{"type":"WEB","url":"https://git.kernel.org/stable/c/4d101016d5e587f820b3ae2d5bb6770d86342649"},{"type":"WEB","url":"https://git.kernel.org/stable/c/708b97e792945d3e4653939fd3405d71a61ad065"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8e0abc17fbd7e305802e84fe98b4950d50f9c433"},{"type":"WEB","url":"https://git.kernel.org/stable/c/adfacfbaeae2cb760f492357cc36b41f84ef7f86"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e48f413c2815787b8cade2795e194e3c4cd782ef"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e6f1a11cfb808441a43ffae9b476cc135732cd27"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63808.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63808"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"ca06197382bde0a3bc20215595d1c9ce20c6e341"},{"fixed":"e6f1a11cfb808441a43ffae9b476cc135732cd27"},{"fixed":"e48f413c2815787b8cade2795e194e3c4cd782ef"},{"fixed":"06c4e1e9967d332ac33ba38b7819851089ff9359"},{"fixed":"8e0abc17fbd7e305802e84fe98b4950d50f9c433"},{"fixed":"4d101016d5e587f820b3ae2d5bb6770d86342649"},{"fixed":"adfacfbaeae2cb760f492357cc36b41f84ef7f86"},{"fixed":"708b97e792945d3e4653939fd3405d71a61ad065"},{"fixed":"3f5f8ee9917cc2b9076ac533492d8a200edcabb8"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-63808.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.7.0"},{"fixed":"5.10.260"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.211"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.177"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.144"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.95"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.38"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.3"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-63808.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"}]}