CVE-2026-43026

Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: ctnetlink: zero expect NAT fields when CTA_EXPECT_NAT absent ctnetlink_alloc_expect() allocates expectations from a non-zeroing slab cache via nf_ct_expect_alloc(). When CTA_EXPECT_NAT is not present in the netlink message, saved_addr and saved_proto are never initialized. Stale data from a previous slab occupant can then be dumped to userspace by ctnetlink_exp_dump_expect(), which checks these fields to decide whether to emit CTA_EXPECT_NAT. The safe sibling nf_ct_expect_init(), used by the packet path, explicitly zeroes these fields. Zero saved_addr, saved_proto and dir in the else branch, guarded by IS_ENABLED(CONFIG_NF_NAT) since these fields only exist when NAT is enabled. Confirmed by priming the expect slab with NAT-bearing expectations, freeing them, creating a new expectation without CTA_EXPECT_NAT, and observing that the ctnetlink dump emits a spurious CTA_EXPECT_NAT containing stale data from the prior allocation.

CVSS v3.1 Score

5.5

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS — Exploit Prediction

0.0001

Probability of exploitation

0.02%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Affected Products

Vendor	Product	Versions
linux	linux_kernel	3.4 — 5.10.253
linux	linux_kernel	5.11 — 5.15.203
linux	linux_kernel	5.16 — 6.1.168
linux	linux_kernel	6.2 — 6.6.134
linux	linux_kernel	6.7 — 6.12.81
linux	linux_kernel	6.13 — 6.18.22
linux	linux_kernel	6.19 — 6.19.12
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/1c2ebdeff8d088a2e47ae25d7b38447249adace2 https://git.kernel.org/stable/c/2898080c054ea4d6ddfaaf21bbedbc229a9a8376 https://git.kernel.org/stable/c/35177c6877134a21315f37d57a5577846225623e https://git.kernel.org/stable/c/929f7a9a7aad9404a5867216c3f8738232355b38 https://git.kernel.org/stable/c/a5a89db6981a1ddf2314bf50cb49db5a3146185f https://git.kernel.org/stable/c/a64b7bf84b4d5ea54218c5d374ec87fff9000f43 https://git.kernel.org/stable/c/bff0f4f06f12d6d9bc565a3e1378abd4f6f5ce36 https://git.kernel.org/stable/c/fd002ff2ea030cbfb0188a11b3c60ce7f84485f4

Frequently Asked Questions

What is CVE-2026-43026? +

In the Linux kernel, the following vulnerability has been resolved: netfilter: ctnetlink: zero expect NAT fields when CTA_EXPECT_NAT absent ctnetlink_alloc_expect() allocates expectations from a non-zeroing slab cache via nf_ct_expect_alloc(). When CTA_EXPECT_NAT is not present in the netlink message, saved_addr and saved_proto are never initialized. Stale data from a previous slab occupant can then be dumped to userspace by ctnetlink_exp_dump_expect(), which checks these fields to decide whether to emit CTA_EXPECT_NAT. The safe sibling nf_ct_expect_init(), used by the packet path, explicitly zeroes these fields. Zero saved_addr, saved_proto and dir in the else branch, guarded by IS_ENABLED(CONFIG_NF_NAT) since these fields only exist when NAT is enabled. Confirmed by priming the expect slab with NAT-bearing expectations, freeing them, creating a new expectation without CTA_EXPECT_NAT, and observing that the ctnetlink dump emits a spurious CTA_EXPECT_NAT containing stale data from the prior allocation. It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2026-43026? +

CVE-2026-43026 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0001, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-43026? +

CVE-2026-43026 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-43026? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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