Gravwell Gravwell Security

GVD-2026-0003 · Third Party advisory

Use-after-free in the Linux kernel during IPv4 TCP connection setup

Advisory
GVD-2026-0003
Severity
Critical
Published
Last updated
CSAF
gvd-2026-0003.json
Markdown
index.md

What you need to do

Self-Hosted

Do these steps on each Linux host that runs Gravwell services or ingesters:

  1. Install the kernel update for CVE-2026-98432 from the vendor of your operating system. On Debian 13, the fixed version is linux 6.12.113-1.
  2. Reboot the host. The fixed kernel runs only after a reboot.
  3. Make sure that uname -r shows the fixed kernel version.

If you run Gravwell in Docker, do these steps on the Docker host. Containers use the kernel of their host.

Gravwell Cloud

No action required from users of Gravwell Cloud services.

If you run edge-deployed ingesters or federators on your own hosts, do the Self-Hosted steps on those hosts.

Vulnerabilities

IdentifierSeverityCVSS 4.0CWEStatusFixed in
CVE-2026-98432Critical9.3CWE-416Under investigation—

CVE-2026-98432Use-after-free in the Linux kernel during IPv4 TCP connection setup

Component
The Linux kernel on hosts that run Gravwell services or ingesters
Status
Under investigation
Affected versions
All versions
CWE
CWE-416: Use After Free

Scores Gravwell's assessment

CVSS 4.0
9.3 Critical CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CVSS 3.1
9.8 Critical CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVE-2026-98432 is a use-after-free in the Linux kernel during IPv4 TCP connection setup. An attacker on the network can trigger the bug without credentials. It affects kernels from 4.4 up to the stable releases that contain the fix. Debian 13 fixes it in linux 6.12.113-1.

On 2026-10-29, the Go security team reported a demonstrated attack that ran code remotely through this bug. The attack used Multipath TCP (MPTCP) connections. Programs built with Go 1.24 or later accept MPTCP connections by default. The Go team states that the bug is not specific to MPTCP. A kernel update is necessary to fix it.

Upstream references

Summary

CVE-2026-98432 is a use-after-free in the Linux kernel during IPv4 TCP connection setup. An attacker on the network can trigger the bug without credentials. On 2026-10-29, the Go security team reported a demonstrated attack that ran code remotely through this bug. The attack used Multipath TCP (MPTCP) connections, which programs built with Go 1.24 or later accept by default. Gravwell builds current releases with Go 1.26.

Self-Hosted customers must install the kernel update from the vendor of their operating system, then reboot each host. No action required from users of Gravwell Cloud services. Gravwell continues to investigate the impact on Gravwell components. When the investigation ends, Gravwell will update this advisory.

Mitigations

If you cannot reboot a host soon, run these commands on that host. They disable MPTCP and restart the Gravwell services.

sudo sysctl -w net.mptcp.enabled=0
sudo systemctl restart 'gravwell_*'

The restart is necessary because a listener that is already open keeps MPTCP until its service restarts.

If a Gravwell container does not use --network host, start it with --sysctl net.mptcp.enabled=0. Such a container has its own network stack. The host setting does not apply to it.

This setting blocks only the demonstrated attack. It does not fix the kernel bug.

Changelog

  1. Initial publication while Gravwell investigates.