# CVE-2026-74722: btrfs: fix memory leak in btrfs_do_encoded_write()

> A memory leak in the Linux kernel's btrfs filesystem allows local attackers to exhaust system memory, causing denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Aug 2026
- **Updated:** 22 Aug 2026
- **Also known as:** AZL-97289, BELL-CVE-2026-74722, DEBIAN-CVE-2026-74722, GHSA-424m-4r3p-f43g, UBUNTU-CVE-2026-74722

## What is CVE-2026-74722?

CVE-2026-74722 is a memory corruption vulnerability in Linux, published on 22 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

btrfs: fix memory leak in btrfs_do_encoded_write()

Local fuzzing of 6.12.94 has found the following memory leak:

Unreferenced object 0xffff888018050a80 (size 64):
  comm "syz.0.17", pid 10297, jiffies 4294953601
  hex dump (first 32 bytes):
    00 10 00 00 00 00 00 00 01 00 00 00 00 00 00 00  ................
    10 0a 05 18 80 88 ff ff 10 0a 05 18 80 88 ff ff  ................
  backtrace (crc a8a6fc29):
    kmemleak_alloc_recursive include/linux/kmemleak.h:42 [inline]
    slab_post_alloc_hook mm/slub.c:4152 [inline]
    slab_alloc_node mm/slub.c:4197 [inline]
    __kmalloc_cache_noprof+0x168/0x2c0 mm/slub.c:4358
    kmalloc_noprof include/linux/slab.h:878 [inline]
    extent_changeset_alloc fs/btrfs/extent_io.h:207 [inline]
    qgroup_reserve_data+0x1c5/0x7d0 fs/btrfs/qgroup.c:4305
    btrfs_qgroup_reserve_data+0x2e/0xb0 fs/btrfs/qgroup.c:4355
    btrfs_do_encoded_write+0x92e/0x1040 fs/btrfs/inode.c:9746
    btrfs_encoded_write fs/btrfs/file.c:1482 [inline]
    btrfs_do_write_iter+0x280/0x610 fs/btrfs/file.c:1507
    btrfs_ioctl_encoded_write+0x3d6/0x490 fs/btrfs/ioctl.c:4738
    btrfs_ioctl+0x6f9/0xc90 fs/btrfs/ioctl.c:-1
    vfs_ioctl fs/ioctl.c:51 [inline]
    __do_sys_ioctl fs/ioctl.c:906 [inline]
    __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:892
    do_syscall_x64 arch/x86/entry/common.c:47 [inline]
    do_syscall_64+0xbe/0x1a0 arch/x86/entry/common.c:78
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

Unreferenced object 0xffff888018050a00 (size 64):
  comm "syz.0.17", pid 10297, jiffies 4294953601
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 ff 0f 00 00 00 00 00 00  ................
    90 0a 05 18 80 88 ff ff 90 0a 05 18 80 88 ff ff  ................
  backtrace (crc cb5c9580):
    kmemleak_alloc_recursive include/linux/kmemleak.h:42 [inline]
    slab_post_alloc_hook mm/slub.c:4152 [inline]
    slab_alloc_node mm/slub.c:4197 [inline]
    __kmalloc_cache_noprof+0x168/0x2c0 mm/slub.c:4358
    kmalloc_noprof include/linux/slab.h:878 [inline]
    kzalloc_noprof include/linux/slab.h:1014 [inline]
    ulist_prealloc+0x9c/0x110 fs/btrfs/ulist.c:114
    extent_changeset_prealloc fs/btrfs/extent_io.h:217 [inline]
    __set_extent_bit+0x16b/0x1a70 fs/btrfs/extent-io-tree.c:1086
    set_record_extent_bits+0x50/0x90 fs/btrfs/extent-io-tree.c:1821
    qgroup_reserve_data+0x274/0x7d0 fs/btrfs/qgroup.c:4312
    btrfs_qgroup_reserve_data+0x2e/0xb0 fs/btrfs/qgroup.c:4355
    btrfs_do_encoded_write+0x92e/0x1040 fs/btrfs/inode.c:9746
    btrfs_encoded_write fs/btrfs/file.c:1482 [inline]
    btrfs_do_write_iter+0x280/0x610 fs/btrfs/file.c:1507
    btrfs_ioctl_encoded_write+0x3d6/0x490 fs/btrfs/ioctl.c:4738
    btrfs_ioctl+0x6f9/0xc90 fs/btrfs/ioctl.c:-1
    vfs_ioctl fs/ioctl.c:51 [inline]
    __do_sys_ioctl fs/ioctl.c:906 [inline]
    __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:892
    do_syscall_x64 arch/x86/entry/common.c:47 [inline]
    do_syscall_64+0xbe/0x1a0 arch/x86/entry/common.c:78
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fix this by freeing an extent changeset before returning from
btrfs_do_encoded_write().

## Which versions are affected by CVE-2026-74722?


## How do I fix CVE-2026-74722?

Apply the vendor's patch.

## Is CVE-2026-74722 being exploited?

There is no known exploitation of CVE-2026-74722 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74722 and fix it if it is affected.

What it is: CVE-2026-74722 is a memory corruption vulnerability in Linux, published on 22 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-74722 in the wild and no public exploit code.

Affected product: Linux. 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-2026-74722/ (Markdown: https://insights.sbomify.com/CVE-2026-74722/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74722
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74722
- OSV: https://osv.dev/vulnerability/CVE-2026-74722

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74722/
Summaries are generated and may contain mistakes; the official description above is the record.