Look up another CVE · open CVE-2026-98108 in the interactive tracker
CVE-2026-98108
Bluetooth: L2CAP: fix chan mode for LE_CONN_REQ + EXT_FLOWCTL pchan
Published 2026-09-25 (24 days ago) by the Linux kernel CNA. Subsystem net/bluetooth. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-98108 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.7-1 | Update the kernel and reboot. Fixed in 7.2.7-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.7-1 | Update the kernel and reboot. Fixed in 7.2.7-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
l2cap_new_connection() sets default value of channel mode to match the parent channel. l2cap_le_connect_req() left this at the default, and created L2CAP_MODE_EXT_FLOWCTL channels if listening pchan has that mode. This causes FLAG_DEFER_SETUP channels to reply to L2CAP_LE_CONN_REQ with L2CAP_ECRED_CONN_RSP, which is incorrect. It can also result to stack OOB write (of l2cap_alloc_cid determined values) in l2cap_ecred_rsp_defer(), as l2cap_le_connect_req() does not limit maximum number of deferred channels or check for duplicate ident. Fix by setting chan->mode correctly in l2cap_le_connect_req(). Also check channel mode in l2cap_ecred_rsp_defer(), and do WARN_ON_ONCE instead of OOB write to make it less brittle.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
net/bluetooth/l2cap_core.c
- What this is
- BLUETOOTH SUBSYSTEMMAINTAINERS section matched on net/bluetooth/ · linux-bluetooth@vger.kernel.org · Supported
- Kernel module
- bluetooth
Check it on the machine
grep -w CONFIG_BT /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w bluetoothPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- trixie, forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64, s390x/s390x
- bookworm · linux-6.12Mnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switch
- CONFIG_BT
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-25 (24 days ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- adjacent network (AV:A)source
- EPSS
- 0.24%, higher than 14.7% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/bluetooth
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.7 | 5.10.271 | ad0f44a3f1f6 |
| 5.7 | 5.15.222 | 564ae0e05e59 |
| 5.7 | 6.1.189 | aab17938998b |
| 5.7 | 6.6.158 | 0e1fc7cab95a |
| 5.7 | 6.12.111 | 1074bcc57f74 |
| 5.7 | 6.18.53 | 5d5a625cbc85 |
| 5.7 | 7.2.7 | 6cb79e649922 |
| 5.7 | 7.3 | 4ef05db5b08b |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:AAttack vector, adjacent network
- The malformed input is a series of L2CAP_LE_CONN_REQ signalling commands, all using the same ident, sent over a BLE link to l2cap_le_connect_req(). The attacker must be within Bluetooth radio range, so the vector is Adjacent.
- AC:HAttack complexity, high
- The OOB write only happens if the target runs an LE listener in BT_MODE_EXT_FLOWCTL with DEFER_SETUP, whose children inherit EXT_FLOWCTL through l2cap_new_connection(). The attacker cannot create that listener. Once it exists, the attacker controls how many LE_CONN_REQs share one ident, and the service's own recvmsg() triggers the write.
- PR:NPrivileges required, none
- l2cap_le_connect_req() only checks the listener's sec_level through smp_sufficient_security(). An LE listener defaults to BT_SECURITY_LOW, so an unpaired peer can open the channels, and Just Works pairing is available otherwise.
- UI:NUser interaction, none
- No human action is needed. The listening service's normal accept/recvmsg on a deferred child calls l2cap_sock_recvmsg(), which then calls __l2cap_ecred_conn_rsp_defer().
- S:UScope, unchanged
- The memory corruption stays within the kernel's own security authority. No VM or hardware isolation boundary is crossed.
- C:HConfidentiality impact, high
- l2cap_ecred_rsp_defer() writes CIDs past the 5-entry scid[] into the adjacent 'count' field, which then steers later writes to attacker-influenced offsets on the kernel stack. Corruption of this kind can be leveraged for disclosure.
- I:HIntegrity impact, high
- This is an out-of-bounds write on the kernel stack in __l2cap_ecred_conn_rsp_defer(). The written values are l2cap_alloc_cid() CIDs whose count and order the attacker influences, and the write can reach the saved frame state.
- A:HAvailability impact, high
- Stack corruption in __l2cap_ecred_conn_rsp_defer() causes a stack-protector panic or an oops, crashing the kernel, and the peer can repeat it.