CVE-2026-74740 net/sched: act_api: fix TOCTOU NULL deref on a->goto_chain
A race condition in the Linux kernel traffic control API allows local attackers to trigger a NULL pointer dereference and cause a system crash.
- 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-2026-74740?
CVE-2026-74740 is a vulnerability in Linux, published on 26 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:
net/sched: act_api: fix TOCTOU NULL deref on a->goto_chain
tcf_action_exec() handles TC_ACT_GOTO_CHAIN by first checking rcu_access_pointer(a->goto_chain) and then calling tcf_action_goto_chain_exec(), which does a second, independent rcu_dereference_bh(a->goto_chain) read and immediately dereferences chain->filter_chain. A concurrent tcf_action_set_ctrlact() (e.g. the gact replace path) can clear a->goto_chain between the two reads, so the second read returns NULL and tcf_action_goto_chain_exec() dereferences NULL.
Fix the race by doing a single rcu_dereference_bh() read of a->goto_chain in tcf_action_exec(), checking it once for NULL, and passing the resulting chain pointer into tcf_action_goto_chain_exec(). This turns the split check/use into a single check/use on one value.
Which versions are affected by CVE-2026-74740?
How do I fix CVE-2026-74740?
Apply the vendor's patch.
Is CVE-2026-74740 being exploited?
There is no known exploitation of CVE-2026-74740 in the wild and no public exploit code.
Sources
Also known as AZL-97746, BELL-CVE-2026-74740, DEBIAN-CVE-2026-74740, UBUNTU-CVE-2026-74740.