# CVE-2025-40044: fs: udf: fix OOB read in lengthAllocDescs handling

> A crafted UDF filesystem image triggers an out-of-bounds read leading to a use-after-free in the Linux kernel, potentially causing crashes or memory disclosure.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 28 Oct 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-68843, BELL-CVE-2025-40044, DEBIAN-CVE-2025-40044, GHSA-4j58-87g3-fv33, ROOT-OS-DEBIAN-11-CVE-2025-40044, ROOT-OS-DEBIAN-12-CVE-2025-40044, ROOT-OS-DEBIAN-13-CVE-2025-40044, ROOT-OS-UBUNTU-2204-CVE-2025-40044, ROOT-OS-UBUNTU-2404-CVE-2025-40044, UBUNTU-CVE-2025-40044

## What is CVE-2025-40044?

CVE-2025-40044 is a high-severity use after free vulnerability in Linux, published on 28 Oct 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

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

fs: udf: fix OOB read in lengthAllocDescs handling

When parsing Allocation Extent Descriptor, lengthAllocDescs comes from
on-disk data and must be validated against the block size. Crafted or
corrupted images may set lengthAllocDescs so that the total descriptor
length (sizeof(allocExtDesc) + lengthAllocDescs) exceeds the buffer,
leading udf_update_tag() to call crc_itu_t() on out-of-bounds memory and
trigger a KASAN use-after-free read.

BUG: KASAN: use-after-free in crc_itu_t+0x1d5/0x2b0 lib/crc-itu-t.c:60
Read of size 1 at addr ffff888041e7d000 by task syz-executor317/5309

CPU: 0 UID: 0 PID: 5309 Comm: syz-executor317 Not tainted 6.12.0-rc4-syzkaller-00261-g850925a8133c #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0x169/0x550 mm/kasan/report.c:488
 kasan_report+0x143/0x180 mm/kasan/report.c:601
 crc_itu_t+0x1d5/0x2b0 lib/crc-itu-t.c:60
 udf_update_tag+0x70/0x6a0 fs/udf/misc.c:261
 udf_write_aext+0x4d8/0x7b0 fs/udf/inode.c:2179
 extent_trunc+0x2f7/0x4a0 fs/udf/truncate.c:46
 udf_truncate_tail_extent+0x527/0x7e0 fs/udf/truncate.c:106
 udf_release_file+0xc1/0x120 fs/udf/file.c:185
 __fput+0x23f/0x880 fs/file_table.c:431
 task_work_run+0x24f/0x310 kernel/task_work.c:239
 exit_task_work include/linux/task_work.h:43 [inline]
 do_exit+0xa2f/0x28e0 kernel/exit.c:939
 do_group_exit+0x207/0x2c0 kernel/exit.c:1088
 __do_sys_exit_group kernel/exit.c:1099 [inline]
 __se_sys_exit_group kernel/exit.c:1097 [inline]
 __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1097
 x64_sys_call+0x2634/0x2640 arch/x86/include/generated/asm/syscalls_64.h:232
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
 </TASK>

Validate the computed total length against epos->bh->b_size.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

## Which versions are affected by CVE-2025-40044?


## How do I fix CVE-2025-40044?

Apply the vendor's patch.

## Is CVE-2025-40044 being exploited?

There is no known exploitation of CVE-2025-40044 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40044 and fix it if it is affected.

What it is: CVE-2025-40044 is a high-severity use after free vulnerability in Linux, published on 28 Oct 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2025-40044 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-2025-40044/ (Markdown: https://insights.sbomify.com/CVE-2025-40044/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40044
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40044
- OSV: https://osv.dev/vulnerability/CVE-2025-40044

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40044/
Summaries are generated and may contain mistakes; the official description above is the record.