CVE-2025-40008: kmsan: fix out-of-bounds access to shadow memory
Vulnerability summary
CVE-2025-40008 is a medium (CVSS 5.7) vulnerability in linux. EPSS estimates a 0.24% chance of exploitation in the next 30 days, higher than 15.6% of scored vulnerabilities.
Not severe (CVSS 5.7, local access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 14 · Related 10Timeline
- 20-10-2025PublishedVulnerability first disclosed.
- 23-05-2026Last modifiedVulnerability information updated.
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.
CVSS metrics
1 score · 1 source · 1 versionEPSS trend
Probability
0.24%
Chance of exploitation in the next 30 days
Percentile
16%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.25% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeNo weakness data has been published for this record.
Affected systems
Known conditions: local access, low-privilege account, no user interaction (CVSS vector). Other conditions: not stated in public data.
Ubuntu121 products
- linux< 6.8.0-106.106 | < 6.17.0-6.6
- linux-allwinner-5.19All versions (No fix recorded)
- linux-aws< 6.8.0-1050.53 | < 6.17.0-1003.3
- linux-aws-5.0All versions (No fix recorded)
- linux-aws-5.11All versions (No fix recorded)
Debian1 product
- linux< 6.1.158-1 | < 6.12.57-1 | < 6.16.10-1
Linux1 product
- linux≥ 9ff078f5bad8990091f1639347de5e02636e9536, < e6684ed39edc35401a3341f85b1ab50a6f89a45d | ≥ 19e85d939001946671643f4c16e1de8c633a6ce0, < df1fa034c0fc229a63d01ffb20bb919b839cb576 | ≥ 2ef3cec44c60ae171b287db7fc2aa341586d65ba, < f84e48707051812289b6c2684d4df2daa9d3bfbc | ≥ 2ef3cec44c60ae171b287db7fc2aa341586d65ba, < 5855792c6bb9a825607845db3feaddaff0414ec3 | ≥ 2ef3cec44c60ae171b287db7fc2aa341586d65ba, < 85e1ff61060a765d91ee62dc5606d4d547d9d105 | abeede7011da6c88e83ed260b909c140b8c9c250 | ≥ 6.1.94, < 6.1.155 | ≥ 6.6.34, < 6.6.109 | ≥ 6.9.5, < 6.10 | 6.10
3 vendors · 123 products
