CVE-2026-31586 | Linux Kernel up to 6.12.82/6.18.23/6.19.13/7.0.0 mm instrumented.h cgwb_release_workfn use after free

VDB-359386 · CVE-2026-31586 · GCVE-0-2026-31586 LINUX KERNEL UP TO 6.12.82/6.18.23/6.19.13/7.0.0 MM INSTRUMENTED.H CGWB_RELEASE_WORKFN USE AFTER FREE HISTORYDIFFRELATEJSONXMLCTI CVSS Meta Temp Score Current Exploit Price (≈) CTI Interest Score 7.6 $5k-$25k 0.57+ Summaryinfo A vulnerability was found in Linux Kernel up to 6.12.82/6.18.23/6.19.13/7.0.0. It has been declared as critical. Impacted is the function cgwb_release_workfn in the library /include/linux/instrumented.h of the component mm. Executing a manipulation can lead to use after free. This vulnerability is handled as CVE-2026-31586. There is not any exploit available. It is recommended to upgrade the affected component. Detailsinfo A vulnerability was found in Linux Kernel up to 6.12.82/6.18.23/6.19.13/7.0.0. It has been declared as critical. This vulnerability affects the function cgwb_release_workfn in the library /include/linux/instrumented.h of the component mm. The manipulation with an unknown input leads to a use after free vulnerability. The CWE definition for the vulnerability is CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes: In the Linux kernel, the following vulnerability has been resolved: mm: blk-cgroup: fix use-after-free in cgwb_release_workfn() cgwb_release_workfn() calls css_put(wb->blkcg_css) and then later accesses wb->blkcg_css again via blkcg_unpin_online(). If css_put() drops the last reference, the blkcg can be freed asynchronously (css_free_rwork_fn -> blkcg_css_free -> kfree) before blkcg_unpin_online() dereferences the pointer to access blkcg->online_pin, resulting in a use-after-free: BUG: KASAN: slab-use-after-free in blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367) Write of size 4 at addr ff11000117aa6160 by task kworker/71:1/531 Workqueue: cgwb_release cgwb_release_workfn Call Trace: blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367) cgwb_release_workfn (mm/backing-dev.c:629) process_scheduled_works (kernel/workqueue.c:3278 kernel/workqueue.c:3385) Freed by task 1016: kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6246 mm/slub.c:6561) css_free_rwork_fn (kernel/cgroup/cgroup.c:5542) process_scheduled_works (kernel/workqueue.c:3302 kernel/workqueue.c:3385) ** Stack based on commit 66672af7a095 ("Add linux-next specific files for 20260410") I am seeing this crash sporadically in Meta fleet across multiple kernel versions. A full reproducer is available at: https://github.com/leitao/debug/blob/main/reproducers/repro_blkcg_uaf.sh (The race window is narrow. To make it easily reproducible, inject a msleep(100) between css_put() and blkcg_unpin_online() in cgwb_release_workfn(). With that delay and a KASAN-enabled kernel, the reproducer triggers the splat reliably in less than a second.) Fix this by moving blkcg_unpin_online() before css_put(), so the cgwb's CSS reference keeps the blkcg alive while blkcg_unpin_online() accesses it. The advisory is available at git.kernel.org. This vulnerability was named CVE-2026-31586 since 03/09/2026. The exploitation appears to be easy. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $5k-$25k at the moment (estimation calculated on 04/24/2026). Upgrading to version 6.12.83, 6.18.24, 6.19.14 or 7.0.1 eliminates this vulnerability. Applying the patch dfc8292a1d6782c76b626315605e0585a5a18447/ea3af09eb87d8f8708c66747fcf1a2762902e839/50879a3c1faf06e661090015d59e2127255cff27/67cb119d32f35e32acd0393bbeb318b2bb1fdafe 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. 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 6.12.10 6.12.11 6.12.12 6.12.13 6.12.14 6.12.15 6.12.16 6.12.17 6.12.18 6.12.19 6.12.20 6.12.21 6.12.22 6.12.23 6.12.24 6.12.25 6.12.26 6.12.27 6.12.28 6.12.29 6.12.30 6.12.31 6.12.32 6.12.33 6.12.34 6.12.35 6.12.36 6.12.37 6.12.38 6.12.39 6.12.40 6.12.41 6.12.42 6.12.43 6.12.44 6.12.45 6.12.46 6.12.47 6.12.48 6.12.49 6.12.50 6.12.51 6.12.52 6.12.53 6.12.54 6.12.55 6.12.56 6.12.57 6.12.58 6.12.59 6.12.60 6.12.61 6.12.62 6.12.63 6.12.64 6.12.65 6.12.66 6.12.67 6.12.68 6.12.69 6.12.70 6.12.71 6.12.72 6.12.73 6.12.74 6.12.75 6.12.76 6.12.77 6.12.78 6.12.79 6.12.80 6.12.81 6.12.82 6.18.0 6.18.1 6.18.2 6.18.3 6.18.4 6.18.5 6.18.6 6.18.7 6.18.8 6.18.9 6.18.10 6.18.11 6.18.12 6.18.13 6.18.14 6.18.15 6.18.16 6.18.17 6.18.18 6.18.19 6.18.20 6.18.21 6.18.22 6.18.23 6.19.0 6.19.1 6.19.2 6.19.3 6.19.4 6.19.5 6.19.6 6.19.7 6.19.8 6.19.9 6.19.10 6.19.11 6.19.12 6.19.13 7.0 License open-source Website Vendor: https://www.kernel.org/ CPE 2.3info 🔒 🔒 🔒 CPE 2.2info 🔒 🔒 🔒 CVSSv4info VulDB Vector: 🔒 VulDB Reliability: 🔍 CVSSv3info VulDB Meta Base Score: 8.0 VulDB Meta Temp Score: 7.6 VulDB Base Score: 8.0 VulDB Temp Score: 7.6 VulDB Vector: 🔒 VulDB Reliability: 🔍 CVSSv2info Vector Complexity Authentication Confidentiality Integrity Availability Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock VulDB Base Score: 🔒 VulDB Temp Score: 🔒 VulDB Reliability: 🔍 Exploitinginfo Class: Use after free CWE: CWE-416 / CWE-119 CAPEC: 🔒 ATT&CK: 🔒 Physical: No Local: No Remote: Partially Availability: 🔒 Status: Not defined Price Prediction: 🔍 Current Price Estimation: 🔒 0-Day Unlock Unlock Unlock Unlock Today Unlock Unlock Unlock Unlock Threat Intelligenceinfo Interest: 🔍 Active Actors: 🔍 Active APT Groups: 🔍 Countermeasuresinfo Recommended: Upgrade Status: 🔍 0-Day Time: 🔒 Upgrade: Kernel 6.12.83/6.18.24/6.19.14/7.0.1 Patch: dfc8292a1d6782c76b626315605e0585a5a18447/ea3af09eb87d8f8708c66747fcf1a2762902e839/50879a3c1faf06e661090015d59e2127255cff27/67cb119d32f35e32acd0393bbeb318b2bb1fdafe Timelineinfo 03/09/2026 CVE reserved 04/24/2026 +45 days Advisory disclosed 04/24/2026 +0 days VulDB entry created 04/24/2026 +0 days VulDB entry last update Sourcesinfo Vendor: kernel.org Advisory: git.kernel.org Status: Confirmed CVE: CVE-2026-31586 (🔒) GCVE (CVE): GCVE-0-2026-31586 GCVE (VulDB): GCVE-100-359386 Entryinfo Created: 04/24/2026 17:48 Changes: 04/24/2026 17:48 (60) Complete: 🔍 Cache ID: 99:ABB:101 Discussion No comments yet. 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