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A New Network Firewall Managed Rule for CVE-2026-98432 Is Here!

Cloudflare Changelog ★★★★ View Markdown
#cloudflare#security#infrastructure

Hi everyone, Shii-chan here! Today I have a security update for you. Cloudflare has prepared a ready-to-use mitigation rule for a Linux kernel vulnerability!

Cloudflare Changelog developers.cloudflare.com

What was announced?

In the Cloudflare Changelog, a new managed rule for Cloudflare Network Firewall was announced. It helps mitigate the Linux IPv4 TCP use-after-free vulnerability (CVE-2026-98432).

Here are the rule details:

  • Rule name: Block CVE-2026-98432 traffic
  • Rule ID: 6a4df2bf984946a88c74b07349557e83
  • Default state: disabled

Why it matters

With kernel-level TCP vulnerabilities, a common question is how to protect yourself at the network edge until patches are applied. When a mitigation ships as a managed rule, you can put it in place through your existing firewall policies without writing your own signatures.

What changes

If you use Network Firewall, you can enable the rule from the dashboard to detect and block traffic related to this vulnerability. Since the rule is disabled by default, you need to turn it on yourself.

Dive Deep

Here are the steps Cloudflare describes:

  • Go to Networking > Firewall Policies > Managed Rulesets
  • Enable the rule with the Log action
  • Review the traffic that matches the rule
  • If the matching traffic is not expected in your environment, change the action to Block

The recommended flow is to watch with Log first instead of blocking right away. That looks like a safeguard to avoid catching legitimate traffic.

The documentation has a separate guide on enabling managed rulesets, and the details of the vulnerability itself are in the Cloudflare Radar Zero Wire briefing, which includes an agent assessment prompt and evidence sources.

Wrap-up

  • Cloudflare Network Firewall now has a managed rule, "Block CVE-2026-98432 traffic", for CVE-2026-98432
  • It targets a use-after-free vulnerability in Linux IPv4 TCP
  • The rule is disabled by default and is enabled from Managed Rulesets under Firewall Policies
  • Check matching traffic with Log first, then switch to Block if it is unexpected

This one is especially useful for infrastructure folks who protect Linux servers with Network Firewall!

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