Bug 2457841 (CVE-2026-31428)

Summary: CVE-2026-31428 kernel: netfilter: nfnetlink_log: fix uninitialized padding leak in NFULA_PAYLOAD
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in the Linux kernel's netfilter component. When manually constructing the NFULA_PAYLOAD netlink attribute, uninitialized padding bytes are not properly cleared. This oversight allows a local user to access stale heap memory contents through the NFLOG netlink socket, leading to information disclosure.
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Description OSIDB Bzimport 2026-04-13 14:02:41 UTC 
In the Linux kernel, the following vulnerability has been resolved:

netfilter: nfnetlink_log: fix uninitialized padding leak in NFULA_PAYLOAD

__build_packet_message() manually constructs the NFULA_PAYLOAD netlink
attribute using skb_put() and skb_copy_bits(), bypassing the standard
nla_reserve()/nla_put() helpers. While nla_total_size(data_len) bytes
are allocated (including NLA alignment padding), only data_len bytes
of actual packet data are copied. The trailing nla_padlen(data_len)
bytes (1-3 when data_len is not 4-byte aligned) are never initialized,
leaking stale heap contents to userspace via the NFLOG netlink socket.

Replace the manual attribute construction with nla_reserve(), which
handles the tailroom check, header setup, and padding zeroing via
__nla_reserve(). The subsequent skb_copy_bits() fills in the payload
data on top of the properly initialized attribute.
Comment 1 Keith Grant 2026-04-13 17:19:02 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026041358-CVE-2026-31428-20a2@gregkh/T