CVE-2026-43027 netfilter: nf_conntrack_helper: pass helper to expect cleanup
A use-after-free in the Linux kernel netfilter subsystem allows attackers to trigger memory corruption, potentially leading to code execution or privilege escalation.
- 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-2026-43027?
CVE-2026-43027 is a high-severity use after free vulnerability in Linux kernel, published on 1 May 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:
netfilter: nf_conntrack_helper: pass helper to expect cleanup
nf_conntrack_helper_unregister() calls nf_ct_expect_iterate_destroy() to remove expectations belonging to the helper being unregistered. However, it passes NULL instead of the helper pointer as the data argument, so expect_iter_me() never matches any expectation and all of them survive the cleanup.
After unregister returns, nfnl_cthelper_del() frees the helper object immediately. Subsequent expectation dumps or packet-driven init_conntrack() calls then dereference the freed exp->helper, causing a use-after-free.
Pass the actual helper pointer so expectations referencing it are properly destroyed before the helper object is freed.
BUG: KASAN: slab-use-after-free in string+0x38f/0x430 Read of size 1 at addr ffff888003b14d20 by task poc/103 Call Trace: string+0x38f/0x430 vsnprintf+0x3cc/0x1170 seq_printf+0x17a/0x240 exp_seq_show+0x2e5/0x560 seq_read_iter+0x419/0x1280 proc_reg_read+0x1ac/0x270 vfs_read+0x179/0x930 ksys_read+0xef/0x1c0 Freed by task 103: The buggy address is located 32 bytes inside of freed 192-byte region [ffff888003b14d00, ffff888003b14dc0)
Weakness: CWE-416
Which versions are affected by CVE-2026-43027?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-43027?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-43027 being exploited?
There is no known exploitation of CVE-2026-43027 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-43027, DEBIAN-CVE-2026-43027, GHSA-f42g-qv35-qm2v, ROOT-OS-DEBIAN-11-CVE-2026-43027, ROOT-OS-UBUNTU-2204-CVE-2026-43027, ROOT-OS-UBUNTU-2404-CVE-2026-43027 and 1 more.