{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-63808", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-07-19T07:54:57.013Z", "datePublished": "2026-07-19T12:02:11.323Z", "dateUpdated": "2026-08-17T04:51:14.402Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-17T04:51:14.402Z" }, "descriptions": [ { "lang": "en", "value": "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->b_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->b_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." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 9.8, "baseSeverity": "CRITICAL" }, "scenarios": [ { "lang": "en", "value": "AV:N - exfat_find_dir_entry() is invoked during VFS directory lookups on mounted exFAT volumes, reachable remotely when that volume is exported via ksmbd or nfsd (common on NAS/router USB shares). A network client resolving paths on the share triggers server-side exfat_lookup without local shell access.\nAC:L - The attacker fully controls the crafted exFAT image to force the TYPE_EXTEND code path and can repeatedly trigger lookups (including concurrent SMB/NFS requests and memory pressure) to win the post-brelse buffer reclaim window. UAF lifetime violations are treated as low complexity per kernel guidance.\nPR:N - Exploitation requires only access to the mounted exFAT filesystem, not real root; guest/anonymous SMB shares on consumer NAS devices and auto-mounted removable media grant unprivileged attackers filesystem access without elevated kernel credentials.\nUI:N - Once a crafted exFAT image is present on a shared or auto-mounted volume, triggering the bug requires only automated path lookups (SMB OPEN/LOOKUP, openat, statx) with no additional victim interaction beyond normal filesystem access.\nS:U - Successful exploitation compromises kernel memory within the same security authority; this is a standard kernel memory corruption issue, not a cross-boundary escape such as VM guest-to-host breakout.\nC:H - The UAF reads freed buffer_head page cache memory through exfat_extract_uni_name(), enabling out-of-bounds kernel heap reads and information disclosure from attacker-influenced reclaimed data.\nI:H - Use-after-free on buffer_head data provides a foundation for heap grooming and arbitrary memory corruption primitives that can be leveraged for kernel code execution and integrity compromise.\nA:H - The bug is a confirmed kernel use-after-free that produced a KASAN fault and page fault oops; even without full exploitation it can cause kernel crashes and denial of service." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/exfat/dir.c" ], "versions": [ { "version": "ca06197382bde0a3bc20215595d1c9ce20c6e341", "lessThan": "e6f1a11cfb808441a43ffae9b476cc135732cd27", "status": "affected", "versionType": "git" }, { "version": "ca06197382bde0a3bc20215595d1c9ce20c6e341", "lessThan": "e48f413c2815787b8cade2795e194e3c4cd782ef", "status": "affected", "versionType": "git" }, { "version": "ca06197382bde0a3bc20215595d1c9ce20c6e341", "lessThan": "06c4e1e9967d332ac33ba38b7819851089ff9359", "status": "affected", "versionType": "git" }, { "version": "ca06197382bde0a3bc20215595d1c9ce20c6e341", "lessThan": "8e0abc17fbd7e305802e84fe98b4950d50f9c433", "status": "affected", "versionType": "git" }, { "version": "ca06197382bde0a3bc20215595d1c9ce20c6e341", "lessThan": "4d101016d5e587f820b3ae2d5bb6770d86342649", "status": "affected", "versionType": "git" }, { "version": "ca06197382bde0a3bc20215595d1c9ce20c6e341", "lessThan": "adfacfbaeae2cb760f492357cc36b41f84ef7f86", "status": "affected", "versionType": "git" }, { "version": "ca06197382bde0a3bc20215595d1c9ce20c6e341", "lessThan": "708b97e792945d3e4653939fd3405d71a61ad065", "status": "affected", "versionType": "git" }, { "version": "ca06197382bde0a3bc20215595d1c9ce20c6e341", "lessThan": "3f5f8ee9917cc2b9076ac533492d8a200edcabb8", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/exfat/dir.c" ], "versions": [ { "version": "5.7", "status": "affected" }, { "version": "0", "lessThan": "5.7", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.260", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.211", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.177", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.144", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.95", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.38", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.1.3", "lessThanOrEqual": "7.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.7", "versionEndExcluding": "5.10.260" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.7", "versionEndExcluding": "5.15.211" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.7", "versionEndExcluding": "6.1.177" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.7", "versionEndExcluding": "6.6.144" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.7", "versionEndExcluding": "6.12.95" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.7", "versionEndExcluding": "6.18.38" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.7", "versionEndExcluding": "7.1.3" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.7", "versionEndExcluding": "7.2" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/e6f1a11cfb808441a43ffae9b476cc135732cd27" }, { "url": "https://git.kernel.org/stable/c/e48f413c2815787b8cade2795e194e3c4cd782ef" }, { "url": "https://git.kernel.org/stable/c/06c4e1e9967d332ac33ba38b7819851089ff9359" }, { "url": "https://git.kernel.org/stable/c/8e0abc17fbd7e305802e84fe98b4950d50f9c433" }, { "url": "https://git.kernel.org/stable/c/4d101016d5e587f820b3ae2d5bb6770d86342649" }, { "url": "https://git.kernel.org/stable/c/adfacfbaeae2cb760f492357cc36b41f84ef7f86" }, { "url": "https://git.kernel.org/stable/c/708b97e792945d3e4653939fd3405d71a61ad065" }, { "url": "https://git.kernel.org/stable/c/3f5f8ee9917cc2b9076ac533492d8a200edcabb8" } ], "title": "exfat: fix potential use-after-free in exfat_find_dir_entry()", "x_generator": { "engine": "bippy-1.2.0" } } } }