CVE-2026-53218
Received Received - Intake
Heap Out-of-Bounds Write in Linux Kernel Netfilter nft_exthdr

Publication date: 2026-06-25

Last updated on: 2026-06-25

Assigner: kernel.org

Description
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.
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Meta Information
Published
2026-06-25
Last Modified
2026-06-25
Generated
2026-06-25
AI Q&A
2026-06-25
EPSS Evaluated
N/A
NVD
CVE-2026-53218
EUVD
EUVD-2026-39309
Affected Vendors & Products
Showing 2 associated CPEs
Vendor Product Version / Range
linux_kernel linux_kernel *
linux linux_kernel *
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Exploitability
CWE
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CWE ID Description
CWE-UNKNOWN
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Executive Summary

This vulnerability exists in the Linux kernel's netfilter nft_exthdr component. Specifically, the function nft_exthdr_init() passes a user-controlled length value to nft_parse_register_store(), which marks that many bytes in a register bitmap as initialized. However, when the NFT_EXTHDR_F_PRESENT flag is set, only 1 or 4 bytes are actually written during evaluation, depending on the path. If the length is greater than 4, registers beyond the first few remain uninitialized, potentially exposing uninitialized stack data from nft_regs.

The fix involves bailing out if userspace requests too much data when the F_PRESENT flag is set, preventing the use of uninitialized data.

Impact Analysis

This vulnerability can lead to the exposure of uninitialized stack data from the nft_regs structure. Since uninitialized data may contain sensitive information, an attacker could potentially access or leak this data, leading to information disclosure.

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