Bug 2464403 (CVE-2026-43026)

Summary: CVE-2026-43026 kernel: netfilter: ctnetlink: zero expect NAT fields when CTA_EXPECT_NAT absent
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in the Linux kernel's netfilter component, specifically within the ctnetlink module. This vulnerability occurs because certain fields are not properly initialized when a new connection tracking expectation is created without the Network Address Translation (NAT) expectation attribute. This oversight can lead to the disclosure of stale data from previously used memory, which a local user could potentially access. This information disclosure could expose sensitive data from the kernel to an unprivileged user.
 Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-05-01 15:04:50 UTC 
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.
Comment 1 Keith Grant 2026-05-01 17:10:49 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050159-CVE-2026-43026-88d7@gregkh/T