CVE-2025-39749 — rcu: Protect ->defer_qs_iw_pending from data race
In the Linux kernel, the following vulnerability has been resolved: rcu: Protect ->defer_qs_iw_pending from data race On kernels built with CONFIG_IRQ_WORK=y, when rcu_read_unlock() is invoked within an interrupts-disabled region of code [1], it will invoke rcu_read_unlock_special(), which uses an irq-work handler to force the system to notice when the RCU read-side critical section actually ends. That end won't happen until interrupts are enabled at the soonest. In some kernels, such as those booted with rcutree.use_softirq=y, the irq-work handler is used unconditionally. The per-CPU rcu_data structure's ->defer_qs_iw_pending field is updated by the irq-work handler and is both read and updated by rcu_read_unlock_special(). This resulted in the following KCSAN splat: ------------------------------------------------------------------------ BUG: KCSAN: data-race in rcu_preempt_deferred_qs_handler / rcu_read_unlock_special read to 0xffff96b95f42d8d8 of 1 bytes by task 90 on cpu 8: rcu_read_unlock_special+0x175/0x260 __rcu_read_unlock+0x92/0xa0 rt_spin_unlock+0x9b/0xc0 __local_bh_enable+0x10d/0x170 __local_bh_enable_ip+0xfb/0x150 rcu_do_batch+0x595/0xc40 rcu_cpu_kthread+0x4e9/0x830 smpboot_thread_fn+0x24d/0x3b0 kthread+0x3bd/0x410 ret_from_fork+0x35/0x40 ret_from_fork_asm+0x1a/0x30 write to 0xffff96b95f42d8d8 of 1 bytes by task 88 on cpu 8: rcu_preempt_deferred_qs_handler+0x1e/0x30 irq_work_single+0xaf/0x160 run_irq_workd+0x91/0xc0 smpboot_thread_fn+0x24d/0x3b0 kthread+0x3bd/0x410 ret_from_fork+0x35/0x40 ret_from_fork_asm+0x1a/0x30 no locks held by irq_work/8/88. irq event stamp: 200272 hardirqs last enabled at (200272): [<ffffffffb0f56121>] finish_task_switch+0x131/0x320 hardirqs last disabled at (200271): [<ffffffffb25c7859>] __schedule+0x129/0xd70 softirqs last enabled at (0): [<ffffffffb0ee093f>] copy_process+0x4df/0x1cc0 softirqs last disabled at (0): [<0000000000000000>] 0x0 ------------------------------------------------------------------------ The problem is that irq-work handlers run with interrupts enabled, which means that rcu_preempt_deferred_qs_handler() could be interrupted, and that interrupt handler might contain an RCU read-side critical section, which might invoke rcu_read_unlock_special(). In the strict KCSAN mode of operation used by RCU, this constitutes a data race on the ->defer_qs_iw_pending field. This commit therefore disables interrupts across the portion of the rcu_preempt_deferred_qs_handler() that updates the ->defer_qs_iw_pending field. This suffices because this handler is not a fast path.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.2% (30-day exploitation probability)+1
- Technical severity (high)+6
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Debian Debian Linux, Linux Linux, Linux Linux Kernel).
- Apply the fixed version or the patch documented under Remediation.
- Search available logs for exploit probes, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Debian | Debian Linux | version 11.0 | Vulnerable | NIST National Vulnerability Database |
| Linux | Linux |
≥ 0864f057b050bc6dd68106b3185e02db5140012d and < 74f58f382a7c8333f8d09701aefaa25913bdbe0eversion 5.3≥ 0864f057b050bc6dd68106b3185e02db5140012d and < 90c09d57caeca94e6f3f87c49e96a91edd40cbfd≥ 0864f057b050bc6dd68106b3185e02db5140012d and < 55e11f6776798b27cf09a7aa0d718415d4fc9cf5≥ 0864f057b050bc6dd68106b3185e02db5140012d and < 90de9c94ea72327cfa9c2c9f6113c23a513af60b≥ 0864f057b050bc6dd68106b3185e02db5140012d and < e35e711c78c8a4c43330c0dcb1c4d507a19c20f4≥ 0864f057b050bc6dd68106b3185e02db5140012d and < b55947b725f190396f475d5d0c59aa855a4d8895≥ 0864f057b050bc6dd68106b3185e02db5140012d and < b5de8d80b5d049f051b95d9b1ee50ae4ab656124 and 2 more≥ 0864f057b050bc6dd68106b3185e02db5140012d and < 0ad84d62217488e679ecc90e8628980dcc003de3≥ 0864f057b050bc6dd68106b3185e02db5140012d and < f937759c7432d6151b73e1393b6517661813d506 |
Vulnerable | CVE Program (cve.org) e CISA ADP |
| Linux | Linux Kernel | ≥ 6.16 and < 6.16.2≥ 6.13 and < 6.15.11≥ 6.7 and < 6.12.43≥ 6.2 and < 6.6.103≥ 5.16 and < 6.1.149≥ 5.11 and < 5.15.190≥ 5.5 and < 5.10.241≥ 5.3 and < 5.4.297 | Vulnerable | NIST National Vulnerability Database |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 7.0 | CVSS 3.1 | High | 1.0 | 5.9 | nvd@nist.gov via NIST National Vulnerability Database |
| 7.0 | CVSS 3.1 | High | — | — | GitHub, Inc. via GitHub Security Advisories |
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H (score shown at the top: nvd@nist.gov) Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · linux/linux
- Record published
- Fix documented
- Affected products added · linux/linux kernel, debian/debian linux
- CVSS changed · 7.0
- Source status changed · → Modified
- Record created in this database
- 2025
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 2× References added · Oct 19, 2026 – Oct 19, 2026
- 1× Official description updated · Oct 19, 2026 – Oct 19, 2026
References
14 on the record
- git.kernel.org/stable/c/b55947b725f190396f475d5d0c59aa855a4d8895
- git.kernel.org/stable/c/74f58f382a7c8333f8d09701aefaa25913bdbe0e
- git.kernel.org/stable/c/55e11f6776798b27cf09a7aa0d718415d4fc9cf5
- git.kernel.org/stable/c/f937759c7432d6151b73e1393b6517661813d506
- git.kernel.org/stable/c/90c09d57caeca94e6f3f87c49e96a91edd40cbfd
- git.kernel.org/stable/c/b5de8d80b5d049f051b95d9b1ee50ae4ab656124
- git.kernel.org/stable/c/0ad84d62217488e679ecc90e8628980dcc003de3
- git.kernel.org/stable/c/e35e711c78c8a4c43330c0dcb1c4d507a19c20f4
- git.kernel.org/stable/c/90de9c94ea72327cfa9c2c9f6113c23a513af60b
- cert-portal.siemens.com/productcert/html/ssa-032379.html
- github.com/advisories/GHSA-5h3j-3mgh-9rr3
- lists.debian.org/debian-lts-announce/2025/10/msg00007.html
- lists.debian.org/debian-lts-announce/2025/10/msg00008.html
- nvd.nist.gov/vuln/detail/CVE-2025-39749
Elsewhere on this site
Related CVEs (same products)
- Unknown CVE-2026-98868 dm-pcache: reject a kset that overruns its segment 1d
- Unknown CVE-2026-98866 sched/cache: Introduce task_struct->sched_cache_grp to fix UAF 1d
- Unknown CVE-2026-98867 dm-pcache: bound the logical key offset from persistent memory 1d
- Unknown CVE-2026-98865 sched_ext: Don't run ops.dequeue() with a DSQ lock held 1d
- Unknown CVE-2026-98864 sched_ext: Wait for SCX_OPSS_DISPATCHING before reenqueueing a task 1d
- Unknown CVE-2026-98863 KVM: x86: Re-pend GET_NESTED_STATE_PAGES if getting said pages fails 1d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No CISA SSVC assessment.
- No CWE classification.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2025-39749 is "rcu: Protect ->defer_qs_iw_pending from data race", rated High. It affects Debian Linux (Debian); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.0 describes technical severity. EPSS 0.17% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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