HIGH
netfilter Flowtable UAF
CVE-2026-23392
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
KernelScan AI7.8HIGH
01Description
In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_tables: release flowtable after rcu grace period on error Call synchronize_rcu() after unregistering the hooks from error path, since a hook that already refers to this flowtable can be already registered, exposing this flowtable to packet path and nfnetlink_hook control plane. This error path is rare, it should only happen by reaching the maximum number hooks or by failing to set up to hardware offload, just call synchronize_rcu(). There is a check for already used device hooks by different flowtable that could result in EEXIST at this late stage. The hook parser can be updated to perform this check earlier to this error path really becomes rarely exercised. Uncovered by KASAN reported as use-after-free from nfnetlink_hook path when dumping hooks.
02KernelScan AI Analysis
Risk summary
A privileged local attacker with network administration capabilities could trigger a use-after-free condition in the kernel's netfilter flowtable handling. This could lead to kernel memory corruption, system crashes, or potentially privilege escalation. The vulnerability requires administrative privileges to exploit but could affect system stability and security.
Vulnerability analysis
Root Cause: In the netfilter nf_tables flowtable creation error path, hooks are unregistered but the flowtable structure can still be accessed by concurrent RCU readers (packet path and nfnetlink_hook control plane) before the RCU grace period expires. This creates a window where freed memory can be accessed.
Attack Surface: This vulnerability affects the netfilter subsystem's flowtable management. It can be triggered through netlink socket operations that create flowtables, specifically when flowtable creation fails due to reaching maximum hook limits or hardware offload setup failures. The attack requires CAP_NET_ADMIN privileges to manipulate netfilter rules and flowtables.
Fix Mechanism: The patch adds a synchronize_rcu() call in the error path after unregistering hooks but before destroying the flowtable structure. This ensures all RCU readers complete their critical sections before the flowtable memory is freed, preventing use-after-free access.
03Fix Versions
| Branch | Fixed in | Patch commit |
|---|---|---|
| 6.1 | 6.1.167 | d2632de96ccb |
| 6.12 | 6.12.78 | 7e3955b282ea |
| 6.18 | 6.18.20 | c8092edb9a11 |
| 6.19 | 6.19.10 | e78a2dcc7cfb |
| 6.6 | 6.6.130 | adee3436ccd2 |
| mainline | 7.0 | d73f4b53aaae |