VulnerabilityPublished 16 Sep 2026Updated 21 Oct 2026

CVE-2026-89956: Linux kernel · s390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev objects

Affects Linux kernelSource CVE Database V5

Not known to be exploited · fixed in 647916988272fe5ecb4bb30cd02b51af9960618a : update Linux kernel when convenient.

Data as of 26 Oct 2026, 13:47 UTC

Severity

Unrated

Rated by Threat Radar · CVSS not yet scored by NVD

EPSS: 0.2% chance of exploitation in 30 days – higher than 10% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 647916988272fe5ecb4bb30cd02b51af9960618a, 530ee1cc71562b6799b9ece187b6c1b757a2c6fa, 22dc712c170efc1a549e3f872467c880be995ac7 +2

Exploitation evidence

Disclosed: evidence found.
CVE published 16 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 2c1ee8983aa377fef4f725162f4f3aa5f9575d4a, < 647916988272fe5ecb4bb30cd02b51af9960618a	Fixed in 647916988272fe5ecb4bb30cd02b51af9960618a
LinuxLinux	Affected ≥ 2c1ee8983aa377fef4f725162f4f3aa5f9575d4a, < 530ee1cc71562b6799b9ece187b6c1b757a2c6fa	Fixed in 530ee1cc71562b6799b9ece187b6c1b757a2c6fa
LinuxLinux	Affected ≥ 2c1ee8983aa377fef4f725162f4f3aa5f9575d4a, < 22dc712c170efc1a549e3f872467c880be995ac7	Fixed in 22dc712c170efc1a549e3f872467c880be995ac7
LinuxLinux	Affected ≥ 2c1ee8983aa377fef4f725162f4f3aa5f9575d4a, < 7fa61c29850d05e40ca9ed41bfdf57673023f581	Fixed in 7fa61c29850d05e40ca9ed41bfdf57673023f581
LinuxLinux	Affected ≥ 2c1ee8983aa377fef4f725162f4f3aa5f9575d4a, < 0fd74477d05743d4cd9b25a3b667daa278d53b93	Fixed in 0fd74477d05743d4cd9b25a3b667daa278d53b93
LinuxLinux	Affected =6.0	Fixed in–

Description

In the Linux kernel, the following vulnerability has been resolved: s390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev objects In order to traverse or add/remove ap_matrix_mdev objects in the matrix_dev->mdev_list, the matrix_dev->guests_lock mutex must be held. There are two functions that access the list without holding the mutex: vfio_ap_mdev_probe function ~~~~~~~~~~~~~~~~~~~~~~~~~~~ The vfio_ap_mdev_probe function uses the matrix_dev->mdevs_lock mutex to guard the add of a newly created ap_matrix_mdev object to the matrix_dev->mdev_list. This mutex does not protect list access; its purpose is to guard against concurrent access to fields contained in an ap_matrix_mdev object. This could lead to kernel memory corruption or use-after-free if another mdev is created or removed concurrently. The adding of an ap_matrix_mdev object to matrix_dev->mdev_list is now guarded by the matrix_dev->guests_lock which is the correct way to protect against concurrent mdev_list access. Also removed the following two lines of code because the matrix_mdev is allocated via vfio_alloc_device macro which uses kzalloc, so req_trigger and cfg_chg_trigger are already zero-initialised when the struct is allocated before the call to vfio_register_emulated_iommu_dev. This prevents a window whereby these triggers are set to NULL after the device is exposed to userspace. matrix_mdev->req_trigger = NULL; matrix_mdev->cfg_chg_trigger = NULL; vfio_ap_mdev_for_queue function ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The status_show function that supports display of the status attribute of the devices in /sys/bus/ap/devices calls the vfio_ap_mdev_for_queue function which iterates the matrix_dev->mdev_list to find the object representing the queue device whose status is to be displayed. In order to traverse this list, the matrix_dev->guests_lock mutex must be held. To fix this, the guests_lock mutex is taken prior to taking the matrix_dev->mdevs_lock mutex in the status_show function. It is taken there rather than the vfio_ap_mdev_for_queue function - where it is needed - because it must be taken prior to the mdevs_lock mutex in order to adhere to the proper locking order and prevent a lockdep splat; also because the mdevs_lock is needed there to access fields within the matrix_mdev object in that function. See the vfio-ap-locking.rst in the linux kernel tree.

References

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