---
id: "CVE-2026-98584"
kind: "vulnerability"
aliases: ["CVE-2026-98584"]
title: "Linux kernel: traffic-control filter dump leaks uninitialised stack bytes to users"
severity: "low"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["linux-kernel", "networking", "runtime", "self-hosted"]
not_affected_if: ["no-local-untrusted-users"]
published_at: "2026-10-18T16:17:10+00:00"
first_seen_at: "2026-10-23T21:57:15+00:00"
updated_at: "2026-10-25T05:23:00+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98584", "first_seen_at": "2026-10-23T21:57:15+00:00"}]
---

# Linux kernel: traffic-control filter dump leaks uninitialised stack bytes to users

The tc classifier text-match dump path copies a stack struct that was not zeroed, so a few uninitialised kernel stack bytes go into the netlink reply. The reporter notes the leaked bytes may not carry sensitive data on production kernels.

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

## How to check

- `uname -r` and compare against the fixed kernel release in your distribution's advisory (unknown from these sources)
- Check whether `tc filter show` is reachable by untrusted local users (unknown from these sources)

## Fix

- Update the Linux kernel to a release that includes the fix zeroing the struct in em_text_dump() (fixed version unknown from these sources)

## Timeline

- 2026-10-23T21:57:15+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98584

## From the sources

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

net/sched: fix potential stack infoleak in em_text_dump()

em_text_dump() allocates struct tcf_em_text on the stack without zeroing
it.  strscpy() writes the algorithm name and a NUL terminator into
conf.algo[], leaving the remaining bytes uninitialised.  nla_put_nohdr()
then copies the full struct to the netlink response.

KMSAN on Linux 7.2-rc6 reports two kernel-infoleak splats from this path,
one triggered via "tc filter show" and one via a raw RTM_GETTFILTER dump:

  BUG: KMSAN: kernel-infoleak in _copy_to_iter+0x1c9/0x2620
    nla_put_nohdr+0x83/0x130
    em_text_dump+0x291/0x550
  Local variable conf created at: em_text_dump+0x5d/0x550
  Bytes 168-179 of 199 are uninitialized

I am not certain whether this constitutes a real security problem in
practice: the test was conducted in a controlled KMSAN environment and
the leaked stack bytes may or may not carry sensitive data on actual
production kernels.  I am reporting it because KMSAN flagged it as a
kernel-infoleak and the fix is straightforward.  I can provide a
userspace reproducer on request.

The original code used strncpy() which zero-pads to the destination size.
Commit b04202d6065c ("net/sched: replace strncpy with strscpy") replaced
it with strscpy(), which does not pad, creating this condition.
Zero-initialising the struct closes it.

---

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