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CVE-2026-74726
bonding: alb: re-check primary_is_promisc under RTNL in bond_alb_monitor
Published 2026-08-22 (2 months ago) by the Linux kernel CNA. Subsystem drivers/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74726 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-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
bond_alb_monitor() reads primary_is_promisc under RCU, then drops RCU and takes RTNL via rtnl_trylock() before undoing the promiscuity it set on the active slave. In that window the active slave can change under RTNL (RTM_DELLINK -> __bond_release_one() -> bond_alb_handle_active_change()), which already drops the promiscuity and clears primary_is_promisc. The monitor still acts on the stale decision: if the slave was removed with no failover, curr_active_slave is now NULL and the deref faults; if it failed over, the stale dev_set_promiscuity(-1) underflows the new slave's promiscuity counter and pins it in IFF_PROMISC. Oops: general protection fault, probably for non-canonical address ... KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] Workqueue: b42 bond_alb_monitor RIP: 0010:bond_alb_monitor (drivers/net/bonding/bond_alb.c:1600) process_one_work (kernel/workqueue.c:3322) worker_thread (kernel/workqueue.c:3486) kthread (kernel/kthread.c:436) ret_from_fork (arch/x86/kernel/process.c:158) Kernel panic - not syncing: Fatal exception Re-check primary_is_promisc (and curr_active_slave) after taking RTNL so the monitor only undoes an increment it still owns. The other bonding monitors already re-read state under RTNL in their commit phase (bond_miimon_commit/bond_ab_arp_commit); bond_alb_monitor() was the only one acting on the pre-trylock decision.
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.
drivers/net/bonding/bond_alb.c
- What this is
- BONDING DRIVERMAINTAINERS section matched on drivers/net/bonding/ · netdev@vger.kernel.org · Maintained
- Kernel module
- bonding
Check it on the machine
grep -w CONFIG_BONDING /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 bondingPrints 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 as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_BONDING
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
- 2026-08-22 (2 months ago)source
- CVSS
- 7.3 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.13%, higher than 2.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.24 | 5.10.265 | f7668762bf5f |
| 2.6.24 | 5.15.216 | 09add8d5cfa9 |
| 2.6.24 | 6.1.183 | b82f51681a7a |
| 2.6.24 | 6.6.152 | dd148539fb47 |
| 2.6.24 | 6.12.104 | dccec0227ed8 |
| 2.6.24 | 6.18.45 | 2faf75a8a065 |
| 2.6.24 | 7.1.9 | 257c4a3a34d8 |
| 2.6.24 | 7.2 | 683c6ba6e58e |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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:LAttack vector, local
- Exploitation requires local RTNL netlink (RTM_DELLINK) or bonding ioctl (SIOCBONDRELEASE) to remove/reconfigure slaves while bond_alb_monitor runs; the bug is in a delayed workqueue, not in packet receive or any remote network protocol path.
- AC:LAttack complexity, low
- An attacker with CAP_NET_ADMIN controls both race sides—timing slave removal/failover against the periodic ALB monitor after primary_is_promisc is set—and can retry rapidly when rtnl_trylock fails, making NULL deref or promiscuity-counter underflow reliably winnable.
- PR:LPrivileges required, low
- Triggering ALB bond setup and slave release requires CAP_NET_ADMIN, which unprivileged users can obtain inside a user+network namespace (unshare -Urn), enabling host-wide kernel panic without init-namespace root on typical distributions.
- UI:NUser interaction, none
- No victim interaction is required; the attacker programmatically creates an ALB bond, drives primary_is_promisc via slave disable/removal, and races bond_alb_monitor without any other user or administrator action.
- S:UScope, unchanged
- Impact is confined to kernel networking state and causes host kernel panic or netdev promiscuity corruption; it does not cross VM, container, or IOMMU security boundaries into another security authority.
- C:HConfidentiality impact, high
- Beyond the NULL-deref crash path, the failover race underflows dev->promiscuity and permanently pins IFF_PROMISC on the new active slave, enabling sustained capture of all traffic on that bonded interface/segment—a broad confidentiality impact on server/cloud HA deployments.
- I:LIntegrity impact, low
- The stale dev_set_promiscuity(-1) corrupts the netdev promiscuity counter (unsigned underflow to a huge value), improperly modifying kernel network device state even though it does not provide arbitrary memory write or code-execution primitives.
- A:HAvailability impact, high
- If the active slave is removed without failover, the monitor dereferences a NULL curr_active_slave and panics the kernel, as confirmed by KASAN null-ptr-deref and "Kernel panic - not syncing: Fatal exception" in the fix commit.