CVE-2021-34999

Kernel-memory disclosure via uninitialized multicast status structures

Published May 7, 2024 · Updated Sep 18, 2024

Information disclosure in OpenBSD Kernel 6.9 allows local users to read kernel memory through multicast-routing sysctls. The IPv4 mrt_sysctl_vif and IPv6 mrt6_sysctl_mif paths copy multicast status structures to userland without first zero-initializing them. Low-privileged code and enabled multicast routing are required; the disclosed bytes can support a separate kernel-privilege escalation chain.

CVSS severity3.8
Low
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in OpenBSD Kernel 6.9 allows local users to read kernel memory through multicast-routing sysctls. The IPv4 mrt_sysctl_vif and IPv6 mrt6_sysctl_mif paths copy multicast status structures to userland without first zero-initializing them. Low-privileged code and enabled multicast routing are required; the disclosed bytes can support a separate kernel-privilege escalation chain.

The record

CVE
CVE-2021-34999
Published
May 7, 2024
Updated
Sep 18, 2024
Vendor
OpenBSD Project
Product
OpenBSD
Classifications
CWE-908, T1005
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 7, 2024CVE publishedPublication date reported by the CVE source.
  2. Sep 18, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <7.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

OpenBSD Project · OpenBSDversion=0 <7.0
OpenBSD Project · OpenBSD Kernelversion=OpenBSD 6.9

Published CVSS scores

3.8Zero Day InitiativeCVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N
5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-908Use of Uninitialized Resource
T1005Data from Local System

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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