CVE-2021-3468

Service hang via unhandled Unix-socket HUP

Published Jun 2, 2021 · Updated Feb 13, 2025

Denial of service in Avahi 0.6 through 0.8 allows local users to hang avahi-daemon via a long line sent to its Unix socket. The client_work function disables input reads when that line fills the buffer, then fails to close the client on HUP, so the kernel repeatedly returns the same event. Access to the local daemon socket is required, and exploitation leaves the service unresponsive in an infinite event loop.

CVSS severity5.5
Medium
EPSS probability0.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Avahi 0.6 through 0.8 allows local users to hang avahi-daemon via a long line sent to its Unix socket. The client_work function disables input reads when that line fills the buffer, then fails to close the client on HUP, so the kernel repeatedly returns the same event. Access to the local daemon socket is required, and exploitation leaves the service unresponsive in an infinite event loop.

The record

CVE
CVE-2021-3468
Published
Jun 2, 2021
Updated
Feb 13, 2025
Vendor
Avahi
Product
Avahi
Classifications
CWE-835, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 2, 2021CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2025Record 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=All avahi versions 0.6 up to 0.8

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Avahi · Avahiversion=All avahi versions 0.6 up to 0.8

Published CVSS scores

2.1NVDAV:L/AC:L/Au:N/C:N/I:N/A:P
5.5GitHubCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
6.2SUSECVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
6.2Amazon LinuxCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499.004Endpoint Denial of Service: Application or System Exploitation

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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