---
id: "CVE-2026-98794"
kind: "vulnerability"
aliases: ["CVE-2026-98794"]
title: "Linux kernel IPVS: backup server accepts malformed sync connection flags"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["ipvs", "linux-kernel", "load-balancer", "runtime", "self-hosted"]
not_affected_if: ["no-ipvs", "no-sync-daemon"]
published_at: "2026-10-18T16:17:33+00:00"
first_seen_at: "2026-10-23T21:57:16+00:00"
updated_at: "2026-10-25T05:15:11+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98794", "first_seen_at": "2026-10-23T21:57:16+00:00"}]
---

# Linux kernel IPVS: backup server accepts malformed sync connection flags

The Linux kernel's IPVS sync handling on a backup server accepted connection flag combinations (NO_CPORT with TEMPLATE, and ONE_PACKE from protocol v0 messages) that can break connection lookups. The sources do not say what an attacker can obtain beyond disruption of the backup server.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- `uname -r` and compare with the fixed kernel version in the vendor advisory: unknown
- `lsmod | grep ip_vs` to see whether IPVS is loaded on the host: unknown

## Fix

- Update the Linux kernel to a release that includes the upstream commit 'ipvs: filter some flags received in the backup server': unknown
- Reboot after the kernel update so the fixed code is running

## Timeline

- 2026-10-23T21:57:16+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98794

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

ipvs: filter some flags received in the backup server

While the IPVS SYNC protocol is not secure by design
we can still protect the backup server from messages that
can wreak havoc.

This commit addresses problems from received connection flags
or their combinations. We now drop messages as follows:

1. the NO_CPORT+TEMPLATE combination allows lookups for normal
connections to hit template which can break in many ways.
While the master does not sync connections with NO_CPORT flag,
i.e. before they are established, we still accept NO_CPORT
without TEMPLATE.

2. ONE_PACKET: it is not sent by master, so we do not
expect it in backup. Before now it was ignored by
IP_VS_CONN_F_BACKUP_MASK for protocol v1 while protocol
v0 created connections that are not hashed and dropped
immediately. Better to apply the IP_VS_CONN_F_BACKUP_MASK
also to the flags from v0 messages for consistency with v1.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_