CVE-2026-63808: exfat: fix potential use-after-free in exfat_find_dir_entry()
In the Linux kernel, the following vulnerability has been resolved:
exfat: fix potential use-after-free in exfatfinddirentry()
In exfatfinddirentry(), the bufferhead obtained from exfatgetdentry() is released with brelse(bh) before the fall-through TYPEEXTEND branch reads the directory entry through ep (which points into bh->bdata):
brelse(bh); if (entrytype == TYPEEXTEND) { ... len = exfatextractuniname(ep, entryuniname); ... }
After brelse() drops our reference, nothing guarantees that the underlying page backing bh->bdata remains valid for the subsequent exfatextractuniname() read. This is the same pattern fixed in commit fc961522ddbd ("exfat: Fix potential use after free in exfatloadupcasetable()").
Move brelse(bh) so it runs after ep is no longer dereferenced on each branch.
Confirmed on QEMU x8664 with CONFIGKASAN=y + CONFIGDEBUGPAGEALLOC=y + CONFIGPAGEPOISONING=y on linux-next, using a crafted exFAT image (long filename with same-hash collisions forcing the TYPEEXTEND path). With a debug-only invalidatebdev() inserted between brelse(bh) and the ep read to make the stale-deref window deterministic, the unpatched kernel faults:
BUG: KASAN: use-after-free in exfatfinddirentry+0x133b/0x15a0 BUG: unable to handle page fault for address: ffff88801a5fa0c2 Oops: 0000 [#1] SMP DEBUGPAGEALLOC KASAN NOPTI RIP: 0010:exfatfinddirentry+0x1188/0x15a0
With this patch applied, the same instrumented harness completes cleanly under the same sanitizer stack. I have not reproduced a crash on an uninstrumented kernel under ordinary reclaim; the instrumented A/B establishes the lifetime violation and that the patch closes it, not an unaided triggerability claim.
Affected Software
Remediation
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Event History
Frequently Asked Questions
What is the severity of CVE-2026-63808?
CVE-2026-63808 has a critical severity rating of 9.8 according to the CVSS v3.1 system.
What type of vulnerability is CVE-2026-63808?
CVE-2026-63808 is categorized as a 'Use After Free' vulnerability in the Linux kernel.
How do I fix CVE-2026-63808?
To fix CVE-2026-63808, you should update your Linux kernel to the latest patched version provided by the Linux Kernel Project.
What potential impact does CVE-2026-63808 have?
CVE-2026-63808 can lead to a denial of service or arbitrary code execution due to a use-after-free condition.
In which component of the Linux kernel does CVE-2026-63808 occur?
CVE-2026-63808 occurs in the exfat filesystem implementation of the Linux kernel.