Linux Kernel up to 6.6.109/6.12.50/6.16.10/6.17.0 cancel_delayed_work use after free

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
7.6	$0-$5k	0.00

Summaryinfo

A vulnerability classified as critical has been found in Linux Kernel up to 6.6.109/6.12.50/6.16.10/6.17.0. This affects the function cancel_delayed_work. The manipulation leads to use after free. This vulnerability is traded as CVE-2025-39996. There is no exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.6.109/6.12.50/6.16.10/6.17.0 and classified as critical. This issue affects the function cancel_delayed_work. The manipulation with an unknown input leads to a use after free vulnerability. Using CWE to declare the problem leads to CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: media: b2c2: Fix use-after-free causing by irq_check_work in flexcop_pci_remove The original code uses cancel_delayed_work() in flexcop_pci_remove(), which does not guarantee that the delayed work item irq_check_work has fully completed if it was already running. This leads to use-after-free scenarios where flexcop_pci_remove() may free the flexcop_device while irq_check_work is still active and attempts to dereference the device. A typical race condition is illustrated below: CPU 0 (remove) | CPU 1 (delayed work callback) flexcop_pci_remove() | flexcop_pci_irq_check_work() cancel_delayed_work() | flexcop_device_kfree(fc_pci->fc_dev) | | fc = fc_pci->fc_dev; // UAF This is confirmed by a KASAN report: ================================================================== BUG: KASAN: slab-use-after-free in __run_timer_base.part.0+0x7d7/0x8c0 Write of size 8 at addr ffff8880093aa8c8 by task bash/135 ... Call Trace: <IRQ> dump_stack_lvl+0x55/0x70 print_report+0xcf/0x610 ? __run_timer_base.part.0+0x7d7/0x8c0 kasan_report+0xb8/0xf0 ? __run_timer_base.part.0+0x7d7/0x8c0 __run_timer_base.part.0+0x7d7/0x8c0 ? __pfx___run_timer_base.part.0+0x10/0x10 ? __pfx_read_tsc+0x10/0x10 ? ktime_get+0x60/0x140 ? lapic_next_event+0x11/0x20 ? clockevents_program_event+0x1d4/0x2a0 run_timer_softirq+0xd1/0x190 handle_softirqs+0x16a/0x550 irq_exit_rcu+0xaf/0xe0 sysvec_apic_timer_interrupt+0x70/0x80 </IRQ> ... Allocated by task 1: kasan_save_stack+0x24/0x50 kasan_save_track+0x14/0x30 __kasan_kmalloc+0x7f/0x90 __kmalloc_noprof+0x1be/0x460 flexcop_device_kmalloc+0x54/0xe0 flexcop_pci_probe+0x1f/0x9d0 local_pci_probe+0xdc/0x190 pci_device_probe+0x2fe/0x470 really_probe+0x1ca/0x5c0 __driver_probe_device+0x248/0x310 driver_probe_device+0x44/0x120 __driver_attach+0xd2/0x310 bus_for_each_dev+0xed/0x170 bus_add_driver+0x208/0x500 driver_register+0x132/0x460 do_one_initcall+0x89/0x300 kernel_init_freeable+0x40d/0x720 kernel_init+0x1a/0x150 ret_from_fork+0x10c/0x1a0 ret_from_fork_asm+0x1a/0x30 Freed by task 135: kasan_save_stack+0x24/0x50 kasan_save_track+0x14/0x30 kasan_save_free_info+0x3a/0x60 __kasan_slab_free+0x3f/0x50 kfree+0x137/0x370 flexcop_device_kfree+0x32/0x50 pci_device_remove+0xa6/0x1d0 device_release_driver_internal+0xf8/0x210 pci_stop_bus_device+0x105/0x150 pci_stop_and_remove_bus_device_locked+0x15/0x30 remove_store+0xcc/0xe0 kernfs_fop_write_iter+0x2c3/0x440 vfs_write+0x871/0xd70 ksys_write+0xee/0x1c0 do_syscall_64+0xac/0x280 entry_SYSCALL_64_after_hwframe+0x77/0x7f ... Replace cancel_delayed_work() with cancel_delayed_work_sync() to ensure that the delayed work item is properly canceled and any executing delayed work has finished before the device memory is deallocated. This bug was initially identified through static analysis. To reproduce and test it, I simulated the B2C2 FlexCop PCI device in QEMU and introduced artificial delays within the flexcop_pci_irq_check_work() function to increase the likelihood of triggering the bug.

The advisory is shared at git.kernel.org. The identification of this vulnerability is CVE-2025-39996 since 04/16/2025. The exploitation is known to be easy. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 02/08/2026).

The vulnerability scanner Nessus provides a plugin with the ID 274816 (Debian dsa-6053 : affs-modules-6.1.0-37-4kc-malta-di - security update), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.6.110, 6.12.51, 6.16.11, 6.17.1 or 6.18-rc1 eliminates this vulnerability. Applying the patch bb10a9ddc8d6c5dbf098f21eb1055a652652e524/514a519baa9e2be7ddc2714bd730bc5a883e1244/3ffabc79388e68877d9c02f724a0b7a38d519daf/6a92f5796880f5aa345f0fed53ef511e3fd6f706/01e03fb7db419d39e18d6090d4873c1bff103914 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 (274816), EUVD (EUVD-2025-34577) and CERT Bund (WID-SEC-2025-2298). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

• Google Container-Optimized OS
• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• RESF Rocky Linux
• Open Source Linux Kernel
• IBM QRadar SIEM
• Dell NetWorker

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.0
• 6.1
• 6.2
• 6.3
• 6.4
• 6.5
• 6.6
• 6.6.109
• 6.7
• 6.8
• 6.9
• 6.10
• 6.11
• 6.12
• 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
• 6.13
• 6.14
• 6.15
• 6.16
• 6.16.0
• 6.16.1
• 6.16.2
• 6.16.3
• 6.16.4
• 6.16.5
• 6.16.6
• 6.16.7
• 6.16.8
• 6.16.9
• 6.16.10
• 6.17.0

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

AV	AC	Au	C	I	A
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳

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

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Nessus ID: 274816
Nessus Name: Debian dsa-6053 : affs-modules-6.1.0-37-4kc-malta-di - security update

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.6.110/6.12.51/6.16.11/6.17.1/6.18-rc1
Patch: bb10a9ddc8d6c5dbf098f21eb1055a652652e524/514a519baa9e2be7ddc2714bd730bc5a883e1244/3ffabc79388e68877d9c02f724a0b7a38d519daf/6a92f5796880f5aa345f0fed53ef511e3fd6f706/01e03fb7db419d39e18d6090d4873c1bff103914

Timelineinfo

04/16/2025 CVE reserved
10/15/2025 +182 days Advisory disclosed
10/15/2025 +0 days VulDB entry created
02/08/2026 +116 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-39996 (🔒)
GCVE (CVE): GCVE-0-2025-39996
GCVE (VulDB): GCVE-100-328649
EUVD: 🔒
CERT Bund: WID-SEC-2025-2298 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 10/15/2025 12:09
Updated: 02/08/2026 20:15
Changes: 10/15/2025 12:09 (58), 10/19/2025 19:00 (1), 10/29/2025 23:05 (1), 11/03/2025 18:47 (7), 11/12/2025 08:28 (2), 11/22/2025 18:08 (1), 12/21/2025 09:10 (1), 02/08/2026 20:15 (1)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Discussion

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