# CVE-2025-71123

## Summary

- **CVE ID:** CVE-2025-71123
- **Severity:** HIGH
- **CVSS Score:** 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Jan 14, 2026
- **Last Modified:** Sep 8, 2026

## Description

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

ext4: fix string copying in parse_apply_sb_mount_options()

strscpy_pad() can't be used to copy a non-NUL-term string into a NUL-term
string of possibly bigger size.  Commit 0efc5990bca5 ("string.h: Introduce
memtostr() and memtostr_pad()") provides additional information in that
regard.  So if this happens, the following warning is observed:

strnlen: detected buffer overflow: 65 byte read of buffer size 64
WARNING: CPU: 0 PID: 28655 at lib/string_helpers.c:1032 __fortify_report+0x96/0xc0 lib/string_helpers.c:1032
Modules linked in:
CPU: 0 UID: 0 PID: 28655 Comm: syz-executor.3 Not tainted 6.12.54-syzkaller-00144-g5f0270f1ba00 #0
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:__fortify_report+0x96/0xc0 lib/string_helpers.c:1032
Call Trace:
 <TASK>
 __fortify_panic+0x1f/0x30 lib/string_helpers.c:1039
 strnlen include/linux/fortify-string.h:235 [inline]
 sized_strscpy include/linux/fortify-string.h:309 [inline]
 parse_apply_sb_mount_options fs/ext4/super.c:2504 [inline]
 __ext4_fill_super fs/ext4/super.c:5261 [inline]
 ext4_fill_super+0x3c35/0xad00 fs/ext4/super.c:5706
 get_tree_bdev_flags+0x387/0x620 fs/super.c:1636
 vfs_get_tree+0x93/0x380 fs/super.c:1814
 do_new_mount fs/namespace.c:3553 [inline]
 path_mount+0x6ae/0x1f70 fs/namespace.c:3880
 do_mount fs/namespace.c:3893 [inline]
 __do_sys_mount fs/namespace.c:4103 [inline]
 __se_sys_mount fs/namespace.c:4080 [inline]
 __x64_sys_mount+0x280/0x300 fs/namespace.c:4080
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x64/0x140 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Since userspace is expected to provide s_mount_opts field to be at most 63
characters long with the ending byte being NUL-term, use a 64-byte buffer
which matches the size of s_mount_opts, so that strscpy_pad() does its job
properly.  Return with error if the user still managed to provide a
non-NUL-term string here.

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

## Affected Products

- Linux — Linux (b2bac84fde28fb6a88817b8b761abda17a1d300b)
- Linux — Linux (e651294218d2684302ee5ed95ccf381646f3e5b4)
- Linux — Linux (01829af7656b56d83682b3491265d583d502e502)
- Linux — Linux (2a0cf438320cdb783e0378570744c0ef0d83e934)
- Linux — Linux (8ecb790ea8c3fc69e77bace57f14cf0d7c177bd8)
- Linux — Linux (7bf46ff83a0ef11836e38ebd72cdc5107209342d)
- Linux — Linux (a6e94557cd05adc82fae0400f6e17745563e5412)
- Linux — Linux (6.18)
- Linux — Linux (0)
- Linux — Linux (5.10.248)
- Linux — Linux (6.1.160)
- Linux — Linux (6.6.120)
- Linux — Linux (6.12.64)
- Linux — Linux (6.18.3)
- Linux — Linux (6.19)
- Linux — Linux (5.10.246)
- Linux — Linux (6.1.158)
- Linux — Linux (6.6.114)
- Linux — Linux (6.12.54)
- Linux — Linux (5.4.301)
- Linux — Linux (6.17.4)

## References

- [CNA](https://git.kernel.org/stable/c/52ac96c4a2dd7bc47666000440b0602d9742e820)
- [CNA](https://git.kernel.org/stable/c/6e37143560e37869d51b7d9e0ac61fc48895f8a0)
- [CNA](https://git.kernel.org/stable/c/902ca2356f1e3ec5355c5808ad5d3f9d0095b0cc)
- [CNA](https://git.kernel.org/stable/c/db9ee13fab0267eccf6544ee35b16c9522db9aac)
- [CNA](https://git.kernel.org/stable/c/5bbacbbf1ca4419861dca3c6b82707c10e9c021c)
- [CNA](https://git.kernel.org/stable/c/ee5a977b4e771cc181f39d504426dbd31ed701cc)
- [siemens-SADP](https://cert-portal.siemens.com/productcert/html/ssa-019113.html)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.17%
- **EPSS Percentile:** 6.3

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-17._