CVE-2021-3502

Local denial of service via reachable assertion

Published May 7, 2021 · Updated Aug 3, 2024

Reachable assertion in Avahi 0.8-5 allows local attackers to crash the avahi service via invalid hostname resolution requests. The avahi_s_host_name_resolver_start function asserts on malformed hostname input received through the Avahi socket or D-Bus methods, terminating the daemon. Local access to those interfaces is required, and the demonstrated consequence is a service availability interruption without confidentiality or integrity impact.

CVSS severity5.5
Medium
EPSS probability0.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reachable assertion in Avahi 0.8-5 allows local attackers to crash the avahi service via invalid hostname resolution requests. The avahi_s_host_name_resolver_start function asserts on malformed hostname input received through the Avahi socket or D-Bus methods, terminating the daemon. Local access to those interfaces is required, and the demonstrated consequence is a service availability interruption without confidentiality or integrity impact.

The record

CVE
CVE-2021-3502
Published
May 7, 2021
Updated
Aug 3, 2024
Vendor
Avahi
Product
Avahi
Classifications
CWE-617, T1499.004
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=0.8-5

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Avahi · Avahiversion=0.8-5

Published CVSS scores

2.1NVDAV:L/AC:L/Au:N/C:N/I:N/A:P
5.5NVDCVSS:3.1/AV:L/AC:L/PR:L/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.

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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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-617Reachable Assertion
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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