CVE-2025-38255: lib/group_cpus: fix NULL pointer dereference from group_cpus_evenly()
Vulnerability summary
CVE-2025-38255 is a medium (CVSS 5.5) NULL Pointer Dereference vulnerability in linux. EPSS estimates a 0.17% chance of exploitation in the next 30 days, higher than 5.4% of scored vulnerabilities.
Advisory lineage
Upstream 0 · Downstream 40 · Related 38Timeline
- 09-07-2025PublishedVulnerability first disclosed.
- 11-05-2026Last modifiedVulnerability information updated.
Description
In the Linux kernel, the following vulnerability has been resolved: lib/group_cpus: fix NULL pointer dereference from group_cpus_evenly() While testing null_blk with configfs, echo 0 > poll_queues will trigger following panic: BUG: kernel NULL pointer dereference, address: 0000000000000010 Oops: Oops: 0000 [#1] SMP NOPTI CPU: 27 UID: 0 PID: 920 Comm: bash Not tainted 6.15.0-02023-gadbdb95c8696-dirty #1238 PREEMPT(undef) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014 RIP: 0010:__bitmap_or+0x48/0x70 Call Trace: <TASK> __group_cpus_evenly+0x822/0x8c0 group_cpus_evenly+0x2d9/0x490 blk_mq_map_queues+0x1e/0x110 null_map_queues+0xc9/0x170 [null_blk] blk_mq_update_queue_map+0xdb/0x160 blk_mq_update_nr_hw_queues+0x22b/0x560 nullb_update_nr_hw_queues+0x71/0xf0 [null_blk] nullb_device_poll_queues_store+0xa4/0x130 [null_blk] configfs_write_iter+0x109/0x1d0 vfs_write+0x26e/0x6f0 ksys_write+0x79/0x180 __x64_sys_write+0x1d/0x30 x64_sys_call+0x45c4/0x45f0 do_syscall_64+0xa5/0x240 entry_SYSCALL_64_after_hwframe+0x76/0x7e Root cause is that numgrps is set to 0, and ZERO_SIZE_PTR is returned from kcalloc(), and later ZERO_SIZE_PTR will be deferenced. Fix the problem by checking numgrps first in group_cpus_evenly(), and return NULL directly if numgrps is zero. [yukuai3@huawei.com: also fix the non-SMP version]
CVSS metrics
3 scores · 3 sources · 1 version- OSV · UbuntuEcosystem advisory · calculated5.5MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- OSV · DebianEcosystem advisory · calculated5.5MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
EPSS trend
Probability
0.17%
Chance of exploitation in the next 30 days
Percentile
5%
Versus all other CVEs
30-day change
Increase +0.02 pp
From 0.14% on 22-09-2026
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 causeAffected systems
Ubuntu120 products
- linux< 6.8.0-100.100
- linux-allwinner-5.19All versions (No fix recorded)
- linux-aws< 6.8.0-1046.49
- linux-aws-5.0All versions (No fix recorded)
- linux-aws-5.11All versions (No fix recorded)
Linux2 products
- linux≥ 6a6dcae8f486c3f3298d0767d34505121c7b0b81, < 64a99eff8dcf1f951a544e6058341b2b19a8fdbd | ≥ 6a6dcae8f486c3f3298d0767d34505121c7b0b81, < 29d39e0d5f16c060e32542b2cf351c09fd22b250 | ≥ 6a6dcae8f486c3f3298d0767d34505121c7b0b81, < 911ef2e8a7de5b2bae8ff11fb0bd01f699e6db65 | ≥ 6a6dcae8f486c3f3298d0767d34505121c7b0b81, < df831e97739405ecbaddb85516bc7d4d1c933d6b | 6.3
- linux_kernel≥ 6.3, < 6.6.96 | ≥ 6.7, < 6.12.36 | ≥ 6.13, < 6.15.5 | 6.16:rc1 | 6.16:rc2 | 6.16:rc3
Debian1 product
- linux< 6.12.37-1
3 vendors · 123 products
