# CVE-2025-40008: linux: In the Linux kernel, the following vulnerability has been resolved:  kmsan: fix out-of-bounds access to shadow memory...

CVE-2025-40008 is fixed in linux on 1 platform, first by DEBIAN-CVE-2025-40008, released October 20, 2025. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2025-40008
- Priority: Routine
- CVSS: n/a
- EPSS: 0.0024
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 20, 2025

## Description

In the Linux kernel, the following vulnerability has been resolved:  kmsan: fix out-of-bounds access to shadow memory  Running sha224_kunit on a KMSAN-enabled kernel results in a crash in kmsan_internal_set_shadow_origin():      BUG: unable to handle page fault for address: ffffbc3840291000     #PF: supervisor read access in kernel mode     #PF: error_code(0x0000) - not-present page     PGD 1810067 P4D 1810067 PUD 192d067 PMD 3c17067 PTE 0     Oops: 0000 [#1] SMP NOPTI     CPU: 0 UID: 0 PID: 81 Comm: kunit_try_catch Tainted: G                 N  6.17.0-rc3 #10 PREEMPT(voluntary)     Tainted: [N]=TEST     Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014     RIP: 0010:kmsan_internal_set_shadow_origin+0x91/0x100     [...]     Call Trace:     <TASK>     __msan_memset+0xee/0x1a0     sha224_final+0x9e/0x350     test_hash_buffer_overruns+0x46f/0x5f0     ? kmsan_get_shadow_origin_ptr+0x46/0xa0     ? __pfx_test_hash_buffer_overruns+0x10/0x10     kunit_try_run_case+0x198/0xa00  This occurs when memset() is called on a buffer that is not 4-byte aligned and extends to the end of a guard page, i.e.  the next page is unmapped.  The bug is that the loop at the end of kmsan_internal_set_shadow_origin() accesses the wrong shadow memory bytes when the address is not 4-byte aligned.  Since each 4 bytes are associated with an origin, it rounds the address and size so that it can access all the origins that contain the buffer.  However, when it checks the corresponding shadow bytes for a particular origin, it incorrectly uses the original unrounded shadow address.  This results in reads from shadow memory beyond the end of the buffer's shadow memory, which crashes when that memory is not mapped.  To fix this, correctly align the shadow address before accessing the 4 shadow bytes corresponding to each origin.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.1.158-1 | [DEBIAN-CVE-2025-40008](https://patchblox.com/security/data/fix/linux/debian-cve-2025-40008.md) | Oct 20, 2025 |
| Linux | linux Debian 13.5 (trixie) | 6.12.57-1 | [DEBIAN-CVE-2025-40008](https://patchblox.com/security/data/fix/linux/debian-cve-2025-40008.md) | Oct 20, 2025 |
| Linux | linux Debian 14 | 6.16.10-1 | [DEBIAN-CVE-2025-40008](https://patchblox.com/security/data/fix/linux/debian-cve-2025-40008.md) | Oct 20, 2025 |

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