MediumCVE-2026-99009

Linux Kernel: security vulnerability (CVE-2026-99009)

Published 23.10.2026Last modified 30.10.2026Sources: BSI, Msrc Update Guide, CVE.org

What is affected, what to do

Update Linux Kernel to version 5.10.273, Linux Kernel to version 5.15.224, Linux Kernel to version 6.1.191.

Affected: Linux Kernel lt 5.10.270..5.10.273
Linux Kernel lt 5.15.221..5.15.224
Linux Kernel lt 6.1.188..6.1.191
Linux Kernel lt 6.6.157..6.6.160
Linux Kernel lt 6.12.109..6.12.114
Linux Kernel lt 6.18.50..6.18.58
Linux Kernel lt 7.2.4..7.2.11
Fixed in: Linux Kernel 5.10.273
Linux Kernel 5.15.224
Linux Kernel 6.1.191
Linux Kernel 6.6.160
Linux Kernel 6.12.114
Linux Kernel 6.18.58
Linux Kernel 7.2.11

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Metrics

4.7

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: Vendor (CNA), CVSS v3

4.7

CVSS v3

Severity Medium on the scale from 0 to 10.

Source: BSI, Msrc Update Guide, CVE.org

0.2 %

EPSS score

Low — model estimates < 1% exploitation likelihood.

Source: FIRST EPSS, percentile 7.3

Show all metrics

Severity: Medium
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 53.92 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: no public PoC known
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 4.7 Methodology
CVSS v3 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 4.7
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 0.2 %; Low — model estimates < 1% exploitation likelihood.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 7.3; Low — this CVE sits in the lower 10% of all CVEs scored today.
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: —
Published: 23.10.2026

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: RFCOMM: connect the session socket without rfcomm_mutex

An RFCOMM connect() issued while a BR/EDR link is being authenticated makes lockdep report a circular dependency, and the reported cycle is a real AB/BA between rfcomm_mutex and hdev->lock.

rfcomm_security_cfm() is called from the HCI event path, which already holds hdev->lock:

hci_rx_work() hci_event_packet() hci_cc_read_enc_key_size() [hdev->lock] hci_encrypt_cfm() [hci_cb_list_lock] rfcomm_security_cfm() [rfcomm_mutex]

while an RFCOMM connect() from userspace takes the same two locks the other way round:

rfcomm_sock_connect() rfcomm_dlc_open() [rfcomm_mutex] __rfcomm_dlc_open() rfcomm_session_create() kernel_connect() l2cap_sock_connect() l2cap_chan_connect() [hdev->lock]

WARNING: possible circular locking dependency detected kworker/u131:1/1128 is trying to acquire lock: rfcomm_mutex, at: rfcomm_security_cfm+0x31/0x3e0 [rfcomm] but task is already holding lock: hci_cb_list_lock, at: hci_cc_read_enc_key_size+0x1d2/0xcc0 Chain exists of: rfcomm_mutex --> &hdev->lock --> hci_cb_list_lock

hci_auth_complete_evt() and hci_encrypt_change_evt() reach the callback the same way.

Both orders have to be seen in the same boot, which is why a BR/EDR connection alone is not enough to show it: a session set up by the remote side is created by rfcomm_accept_connection() in krfcommd, which calls kernel_accept() and never takes hdev->lock under rfcomm_mutex. Connecting a device that authenticates and encrypts the link and then calling connect() on an RFCOMM socket towards any address - the connect does not have to succeed, the order is recorded before the page timeout

reports it every time.

Only the session socket has to be connected with the lock held, and it does not: nothing else can see the socket before it is put on the session list. So connect it first and take rfcomm_mutex afterwards, which removes the rfcomm_mutex -> hdev->lock order for good, rather than keeping the HCI event path out of rfcomm_mutex.

rfcomm_session_create() becomes rfcomm_session_connect(), which returns the connected socket without touching the session list, and rfcomm_dlc_open() adds the session once it holds the lock again. If another opener added a session for the same pair while this socket was connecting, that session is used and this socket is dropped. __rfcomm_dlc_open() now takes the session it should use, and its state check runs after the lock is re-acquired, so a DLC that was opened or closed in the meantime is still handled.

Over an existing ACL link the connection can complete before the session reaches the list, and the wakeup from the socket callback is then lost, so krfcommd is woken once the session is visible.

Connecting without the lock opens a window in which the socket can be closed. The DLC is not on a session yet, so rfcomm_dlc_close() finds nothing to do and returns without touching it, and rfcomm_dlc_open() would then attach a DLC whose owner is gone. rfcomm_dlc_close() now marks such a DLC with RFCOMM_CLOSED, and rfcomm_dlc_open() checks the mark once it holds rfcomm_mutex again and drops the socket instead of attaching the DLC. The mark is cleared when an open starts, so a DLC that is reused is not affected. This covers both callers of rfcomm_dlc_open(), the socket and the tty layer.

Source: BSI CSAF, BSI WID Portal, Microsoft Security Update Guide, cvelistv5, NVD (NIST)

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
Linux	Linux	`6.12.109 – < 6.12.114` `5.10.270 – < 5.10.273` `6.6.157 – < 6.6.160` `6.1.188 – < 6.1.191` `7.2.4 – < 7.2.11` `5.15.221 – < 5.15.224` `6.18.50 – < 6.18.58`	`6.12.114` `5.10.273` `6.6.160` `6.1.191` `7.2.11` `5.15.224` `6.18.58`

Vendors and products

Linux Linux

References & sources

git.kernel.orgstable/c/4dc3d5a004b8fd59f3c905631dbb18cb601b1b41
git.kernel.orgstable/c/ac022970e9fb0a5f7e7d1f6c8e104c1ed924dd1c
git.kernel.orgstable/c/cc7732b8549ecb6f02457edeb8db1f6d255e381c
git.kernel.orgstable/c/d2206e8c78be69d21d4f5343c3e99fbaeef41cbb
git.kernel.orgstable/c/f492de11b325446b0b11bc2eb86e1f546eaa61b6
git.kernel.orgstable/c/172b152119643018a2ed792e5096f33a4491c7de
git.kernel.orgstable/c/caf78390f78a005d5cdc1db2eb467b2794bbf020
git.kernel.orgstable/c/d7a3bf6f55ab77d465206b25fe3418091c3d4b92

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

30.10.2026Record modifiedLinux

New references:

Show 4 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/99xxx/CVE-2026-99009.json">CVE-2026-99009</a>
Reference	added	—	https://git.kernel.org/stable/c/172b152119643018a2ed792e5096f33a4491c7de
Reference	added	—	https://git.kernel.org/stable/c/caf78390f78a005d5cdc1db2eb467b2794bbf020
Reference	added	—	https://git.kernel.org/stable/c/d7a3bf6f55ab77d465206b25fe3418091c3d4b92

Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

23.10.2026ReceivedLinux

Description added or changed

New references:

and 1 more reference

Show 7 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Description	added	—	In the Linux kernel, the following vulnerability has been resolved: Bluetooth: RFCOMM: connect the session socket without rfcomm_mutex An RFCOMM connect() issued while a BR/EDR link is being authenticated makes lockdep report a circular dependency, and the reported cycle is a real AB/BA between rfcomm_mutex and hdev->lock. rfcomm_security_cfm() is called from the HCI event path, which already holds hdev->lock: hci_rx_work() hci_event_packet() hci_cc_read_enc_key_size() [hdev->lock] hci_encrypt_cfm() [hci_cb_list_lock] rfcomm_security_cfm() [rfcomm_mutex] while an RFCOMM connect() from userspace takes the same two locks the other way round: rfcomm_sock_connect() rfcomm_dlc_open() [rfcomm_mutex] __rfcomm_dlc_open() rfcomm_session_create() kernel_connect() l2cap_sock_connect() l2cap_chan_connect() [hdev->lock] WARNING: possible circular locking dependency detected kworker/u131:1/1128 is trying to acquire lock: rfcomm_mutex, at: rfcomm_security_cfm+0x31/0x3e0 [rfcomm] but task is already holding lock: hci_cb_list_lock, at: hci_cc_read_enc_key_size+0x1d2/0xcc0 Chain exists of: rfcomm_mutex --> &hdev->lock --> hci_cb_list_lock hci_auth_complete_evt() and hci_encrypt_change_evt() reach the callback the same way. Both orders have to be seen in the same boot, which is why a BR/EDR connection alone is not enough to show it: a session set up by the remote side is created by rfcomm_accept_connection() in krfcommd, which calls kernel_accept() and never takes hdev->lock under rfcomm_mutex. Connecting a device that authenticates and encrypts the link and then calling connect() on an RFCOMM socket towards any address - the connect does not have to succeed, the order is recorded before the page timeout - reports it every time. Only the session socket has to be connected with the lock held, and it does not: nothing else can see the socket before it is put on the session list. So connect it first and take rfcomm_mutex afterwards, which removes the rfcomm_mutex -> hdev->lock order for good, rather than keeping the HCI event path out of rfcomm_mutex. rfcomm_session_create() becomes rfcomm_session_connect(), which returns the connected socket without touching the session list, and rfcomm_dlc_open() adds the session once it holds the lock again. If another opener added a session for the same pair while this socket was connecting, that session is used and this socket is dropped. __rfcomm_dlc_open() now takes the session it should use, and its state check runs after the lock is re-acquired, so a DLC that was opened or closed in the meantime is still handled. Over an existing ACL link the connection can complete before the session reaches the list, and the wakeup from the socket callback is then lost, so krfcommd is woken once the session is visible. Connecting without the lock opens a window in which the socket can be closed. The DLC is not on a session yet, so rfcomm_dlc_close() finds nothing to do and returns without touching it, and rfcomm_dlc_open() would then attach a DLC whose owner is gone. rfcomm_dlc_close() now marks such a DLC with RFCOMM_CLOSED, and rfcomm_dlc_open() checks the mark once it holds rfcomm_mutex again and drops the socket instead of attaching the DLC. The mark is cleared when an open starts, so a DLC that is reused is not affected. This covers both callers of rfcomm_dlc_open(), the socket and the tty layer.
Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/99xxx/CVE-2026-99009.json">CVE-2026-99009</a>
Reference	added	—	https://git.kernel.org/stable/c/4dc3d5a004b8fd59f3c905631dbb18cb601b1b41
Reference	added	—	https://git.kernel.org/stable/c/ac022970e9fb0a5f7e7d1f6c8e104c1ed924dd1c
Reference	added	—	https://git.kernel.org/stable/c/cc7732b8549ecb6f02457edeb8db1f6d255e381c
Reference	added	—	https://git.kernel.org/stable/c/d2206e8c78be69d21d4f5343c3e99fbaeef41cbb
Reference	added	—	https://git.kernel.org/stable/c/f492de11b325446b0b11bc2eb86e1f546eaa61b6

Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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