# CVE-2026-63796: ocfs2: reject oversized group bitmap descriptors

> A malicious OCFS2 filesystem image can trigger a use-after-free in the kernel, potentially causing a crash or arbitrary code execution.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jul 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-63796, DEBIAN-CVE-2026-63796, GHSA-9923-9mc9-hq5v, ROOT-OS-DEBIAN-11-CVE-2026-63796, ROOT-OS-UBUNTU-2204-CVE-2026-63796, UBUNTU-CVE-2026-63796

## What is CVE-2026-63796?

CVE-2026-63796 is a high-severity memory corruption vulnerability in Linux kernel, published on 19 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ocfs2: reject oversized group bitmap descriptors

ocfs2_validate_gd_parent() only bounds bg_bits against the parent
allocator's chain geometry.  A malicious descriptor can still claim a
bg_size/bg_bits pair that exceeds the bitmap bytes that physically fit in
the group descriptor block, so later bitmap scans and bit updates can run
past bg_bitmap.

Add a physical-cap check based on ocfs2_group_bitmap_size() for the parent
allocator type and reject descriptors whose bg_size or bg_bits exceed that
capacity.  Keep the existing chain geometry check so both the on-disk
bitmap layout and the allocator metadata must agree before the descriptor
is used.

Validation reproduced this kernel report:
KASAN use-after-free in _find_next_bit+0x7f/0xc0
Read of size 8
Call trace:
  dump_stack_lvl+0x66/0xa0 (?:?)
  print_report+0xd0/0x630 (?:?)
  _find_next_bit+0x7f/0xc0 (?:?)
  srso_alias_return_thunk+0x5/0xfbef5 (?:?)
  __virt_addr_valid+0x188/0x2f0 (?:?)
  kasan_report+0xe4/0x120 (?:?)
  ocfs2_find_max_contig_free_bits+0x35/0x70 (fs/ocfs2/suballoc.c:1375)
  ocfs2_block_group_set_bits+0x472/0x4b0 (fs/ocfs2/suballoc.c:1457)
  ocfs2_cluster_group_search+0x16b/0x440 (fs/ocfs2/suballoc.c:86)
  ocfs2_bg_discontig_fix_result+0x1ef/0x230 (fs/ocfs2/suballoc.c:1786)
  ocfs2_search_chain+0x8f8/0x10a0 (fs/ocfs2/suballoc.c:1886)
  get_page_from_freelist+0x70e/0x2370 (?:?)
  lock_release+0xc6/0x290 (?:?)
  do_raw_spin_unlock+0x9a/0x100 (?:?)
  kasan_unpoison+0x27/0x60 (?:?)
  __bfs+0x147/0x240 (?:?)
  get_page_from_freelist+0x83d/0x2370 (?:?)
  ocfs2_claim_suballoc_bits+0x38c/0xe70 (fs/ocfs2/suballoc.c:96)
  sched_domains_numa_masks_clear+0x70/0xd0 (?:?)
  check_irq_usage+0xe8/0xb70 (?:?)
  __ocfs2_claim_clusters+0x18d/0x4c0 (fs/ocfs2/suballoc.c:2497)
  check_path+0x24/0x50 (?:?)
  rcu_is_watching+0x20/0x50 (?:?)
  check_prev_add+0xfd/0xd00 (?:?)
  ocfs2_add_clusters_in_btree+0x17d/0x810 (fs/ocfs2/suballoc.c:?)
  __folio_batch_add_and_move+0x1f5/0x3d0 (?:?)
  ocfs2_add_inode_data+0xd9/0x120 (fs/ocfs2/suballoc.c:?)
  filemap_add_folio+0x105/0x1f0 (?:?)
  ocfs2_write_begin_nolock+0x29f7/0x2f80 (fs/ocfs2/suballoc.c:3043)
  ocfs2_read_inode_block+0xb5/0x110 (fs/ocfs2/suballoc.c:?)
  down_write+0xf5/0x180 (?:?)
  ocfs2_write_begin+0x180/0x240 (fs/ocfs2/suballoc.c:?)
  __mark_inode_dirty+0x758/0x9a0 (?:?)
  inode_to_bdi+0x41/0x90 (?:?)
  balance_dirty_pages_ratelimited_flags+0xf8/0x1d0 (?:?)
  generic_perform_write+0x252/0x440 (?:?)
  mnt_put_write_access_file+0x16/0x70 (?:?)
  file_update_time_flags+0xe4/0x200 (?:?)
  ocfs2_file_write_iter+0x80a/0x1320 (fs/ocfs2/suballoc.c:?)
  lock_acquire+0x184/0x2f0 (?:?)
  ksys_write+0xd2/0x170 (?:?)
  apparmor_file_permission+0xf5/0x310 (?:?)
  read_zero+0x8d/0x140 (?:?)
  lock_is_held_type+0x8f/0x100 (?:?)

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-63796?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-63796?

Apply the vendor's patch.

## Is CVE-2026-63796 being exploited?

There is no known exploitation of CVE-2026-63796 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63796 and fix it if it is affected.

What it is: CVE-2026-63796 is a high-severity memory corruption vulnerability in Linux kernel, published on 19 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-63796 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-63796/ (Markdown: https://insights.sbomify.com/CVE-2026-63796/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63796
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63796
- OSV: https://osv.dev/vulnerability/CVE-2026-63796

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63796/
Summaries are generated and may contain mistakes; the official description above is the record.