CVE-2026-74726 bonding: alb: re-check primary_is_promisc under RTNL in bond_alb_monitor
A race condition in the Linux kernel bonding driver allows a local attacker to trigger a kernel panic via a null pointer dereference.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-74726?
CVE-2026-74726 is a high-severity vulnerability in Linux, published on 22 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
bonding: alb: re-check primary_is_promisc under RTNL in bond_alb_monitor
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.
Which versions are affected by CVE-2026-74726?
How do I fix CVE-2026-74726?
Apply the vendor's patch.
Is CVE-2026-74726 being exploited?
There is no known exploitation of CVE-2026-74726 in the wild and no public exploit code.
Sources
Also known as AZL-97266, BELL-CVE-2026-74726, DEBIAN-CVE-2026-74726, GHSA-33v4-fjq4-gjwg, UBUNTU-CVE-2026-74726.