Summary
In the Linux kernel, the following vulnerability has been resolved: io_uring/sqpoll: zero sqd-...
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.
Impact
Memory is accessed after it has been freed, leading to undefined behavior in native code. Typical impact: memory corruption, crash, or potential code execution.
CVE-2025-21633 has a CVSS score of 7.8 (High). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2025-21633? CVE-2025-21633 is a high-severity use after free vulnerability. No fixed version is listed yet. Memory is accessed after it has been freed, leading to undefined behavior in native code.
- How severe is CVE-2025-21633? CVE-2025-21633 has a CVSS score of 7.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Is there a fix for CVE-2025-21633? No fixed version is listed for CVE-2025-21633 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2025-21633 exploitable, and should I be worried? Whether CVE-2025-21633 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-21633 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.