Bug 2492721 (CVE-2026-53218)

Summary: CVE-2026-53218 kernel: netfilter: nft_exthdr: fix register tracking for F_PRESENT flag
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's netfilter component. This vulnerability occurs in the `nft_exthdr` module when handling user-controlled data lengths with a specific flag, `NFT_EXTHDR_F_PRESENT`, enabled. An attacker could exploit this by providing a crafted input, leading to the exposure of uninitialized stack memory. This information disclosure could potentially reveal sensitive system data.
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Description OSIDB Bzimport 2026-06-25 10:02:18 UTC 
In the Linux kernel, the following vulnerability has been resolved:

netfilter: nft_exthdr: fix register tracking for F_PRESENT flag

nft_exthdr_init() passes user-controlled priv->len to
nft_parse_register_store(), which marks that many bytes in the
register bitmap as initialized.  However, when NFT_EXTHDR_F_PRESENT
is set, the eval paths write only 1 byte (nft_reg_store8) or
4 bytes (*dest = 0 on TCP/DCCP error path).  When len > 4,
registers beyond the first are never written, retaining
uninitialized stack data from nft_regs.

Bail out if userspace requests too much data when F_PRESENT is set.
Comment 1 Mauro Matteo Cascella 2026-06-26 09:31:35 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026062505-CVE-2026-53218-d36e@gregkh/T