HIGH
netfilter ctnetlink Expectation OOB
CVE-2026-43025
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H
KernelScan AI7.3HIGH
01Description
In the Linux kernel, the following vulnerability has been resolved: netfilter: ctnetlink: ignore explicit helper on new expectations Use the existing master conntrack helper, anything else is not really supported and it just makes validation more complicated, so just ignore what helper userspace suggests for this expectation. This was uncovered when validating CTA_EXPECT_CLASS via different helper provided by userspace than the existing master conntrack helper: BUG: KASAN: slab-out-of-bounds in nf_ct_expect_related_report+0x2479/0x27c0 Read of size 4 at addr ffff8880043fe408 by task poc/102 Call Trace: nf_ct_expect_related_report+0x2479/0x27c0 ctnetlink_create_expect+0x22b/0x3b0 ctnetlink_new_expect+0x4bd/0x5c0 nfnetlink_rcv_msg+0x67a/0x950 netlink_rcv_skb+0x120/0x350 Allowing to read kernel memory bytes off the expectation boundary. CTA_EXPECT_HELP_NAME is still used to offer the helper name to userspace via netlink dump.
02KernelScan AI Analysis
Risk summary
A privileged local attacker with CAP_NET_ADMIN can trigger an out-of-bounds read in the netfilter conntrack expectation handling code, potentially leaking sensitive kernel memory. While this requires elevated privileges, it could be used to bypass KASLR or extract other sensitive information from kernel memory.
Vulnerability analysis
Root Cause: The vulnerability occurs when userspace provides a different helper via CTA_EXPECT_HELP_NAME than the existing master conntrack helper. The code attempts to validate CTA_EXPECT_CLASS using the userspace-provided helper instead of the master conntrack's helper, leading to inconsistent state and out-of-bounds memory access during expectation processing.
Attack Surface: This vulnerability is exploitable through the netfilter netlink interface (nfnetlink), which requires CAP_NET_ADMIN privileges. An attacker with these privileges can craft malicious netlink messages to trigger the out-of-bounds read, potentially leaking kernel memory contents.
Fix Mechanism: The fix simplifies the logic by ignoring any explicit helper provided by userspace for new expectations and always using the existing master conntrack helper. This eliminates the validation complexity and prevents the mismatch that caused the out-of-bounds read. The CTA_EXPECT_HELP_NAME attribute is still preserved for netlink dumps to userspace.
03Fix Versions
| Branch | Fixed in | Patch commit |
|---|---|---|
| 6.1 | 6.1.168 | e135f8e8212c |
| 6.12 | 6.12.81 | 0f6c33697ccf |
| 6.18 | 6.18.22 | 187b6ec5229e |
| 6.19 | 6.19.12 | 21a04c31db40 |
| 6.6 | 6.6.134 | 2ea0f35f235f |
| mainline | 7.0 | 917b61fa2042 |