CVE-2021-3502

Exp

A flaw was found in avahi 0.8-5. A reachable assertion is present in avahi_s_host_name_resolver_start function allowing a local attacker to crash the avahi service by requesting hostname resolutions through the avahi socket or dbus methods for invalid hostnames. The highest threat from this vulnerability is to the service availability.

Published: 2021-05-07 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-3502 is rated Exploit Available (50/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.37%). 2 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-3502

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-3502

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.04% 0.37% +0.33%
2 2025-03-30 0.07% 0.04% -0.03%
3 2025-03-29 — 0.07% —

Full EPSS history (10 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3502

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.5 3.1 MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 3.6 [email protected]
2.1 2.0 LOW
AV:L/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:L)
Requires local access to the target system.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 3.9 2.9 [email protected]

Weakness enumeration for CVE-2021-3502

OS Trackers for CVE-2021-3502

vendor priority summary link
alpine medium CVE-2021-3502: 1 source package rows (avahi); 6 state rows across 6 repos (3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 6, open 0. https://security.alpinelinux.org/vuln/CVE-2021-3502
debian not yet assigned CVE-2021-3502 not yet assigned priority: Debian including 1 source packages (avahi), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-3502
redhat medium — https://access.redhat.com/security/cve/CVE-2021-3502
suse medium CVE-2021-3502 severity moderate: SUSE including 154 source package names (avahi, avahi-0.8-15.el9, …), 424 product×package rows across 53 product lines (HPE Helion OpenStack 8, SUSE CaaS Platform 4.0, … (53 product lines)): Known Not Affected 266, Fixed 158. https://www.suse.com/security/cve/CVE-2021-3502/
ubuntu medium CVE-2021-3502 medium priority: Ubuntu including 1 source packages (avahi), 9 status rows across 9 suites (bionic, focal, groovy, hirsute, impish, jammy, trusty, upstream, xenial): not-affected 4, released 4, needs-triage 1. https://ubuntu.com/security/CVE-2021-3502

Affected software / configurations for CVE-2021-3502

Vendor Product Version Raw CPE
avahi avahi 0.8-5 cpe:2.3:a:avahi:avahi:0.8-5:*:*:*:*:*:*:*

References for CVE-2021-3502

URL Tags
https://bugzilla.redhat.com/show_bug.cgi?id=1946914 Exploit Issue Tracking Patch Third Party Advisory
https://github.com/lathiat/avahi/issues/338 Exploit Third Party Advisory
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