Linux Kernel up to 6.12.9/6.13-rc6 sqpoll thread_group_cputime use after free

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.12.9/6.13-rc6. It has been classified as critical. The impacted element is the function thread_group_cputime of the component sqpoll. Performing a manipulation results in use after free. This vulnerability was named CVE-2025-21633. There is no available exploit. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability classified as critical has been found in Linux Kernel up to 6.12.9/6.13-rc6. This affects the function thread_group_cputime of the component sqpoll. The manipulation with an unknown input leads to a use after free vulnerability. CWE is classifying the issue as CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: io_uring/sqpoll: zero sqd->thread on tctx errors Syzkeller reports: BUG: KASAN: slab-use-after-free in thread_group_cputime+0x409/0x700 kernel/sched/cputime.c:341 Read of size 8 at addr ffff88803578c510 by task syz.2.3223/27552 Call Trace: ... kasan_report+0x143/0x180 mm/kasan/report.c:602 thread_group_cputime+0x409/0x700 kernel/sched/cputime.c:341 thread_group_cputime_adjusted+0xa6/0x340 kernel/sched/cputime.c:639 getrusage+0x1000/0x1340 kernel/sys.c:1863 io_uring_show_fdinfo+0xdfe/0x1770 io_uring/fdinfo.c:197 seq_show+0x608/0x770 fs/proc/fd.c:68 ... That's due to sqd->task not being cleared properly in cases where SQPOLL task tctx setup fails, which can essentially only happen with fault injection to insert allocation errors.

It is possible to read the advisory at git.kernel.org. This vulnerability is uniquely identified as CVE-2025-21633 since 12/29/2024. The exploitability is told to be difficult. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 02/17/2026).

The vulnerability scanner Nessus provides a plugin with the ID 233479 (Ubuntu 24.10 : Linux kernel (Low Latency) vulnerabilities (USN-7380-1)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.12.10 or 6.13-rc7 eliminates this vulnerability. Applying the patch aa7496d668c30ca7421b3bfdcd948ee861a13d17/4b7cfa8b6c28a9fa22b86894166a1a34f6d630ba is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (233479) and CERT Bund (WID-SEC-2025-0119). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Affected

• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• RESF Rocky Linux
• Dell NetWorker
• Dell Avamar
• Dell PowerProtect Data Domain
• Open Source Linux Kernel
• Dell Secure Connect Gateway

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.12.0
• 6.12.1
• 6.12.2
• 6.12.3
• 6.12.4
• 6.12.5
• 6.12.6
• 6.12.7
• 6.12.8
• 6.12.9
• 6.13-rc1
• 6.13-rc2
• 6.13-rc3
• 6.13-rc4
• 6.13-rc5
• 6.13-rc6

License

• open-source

Website

• Vendor: https://www.kernel.org/

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