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NVD / CVE Program· CNA redhat

CVE-2021-3502: A flaw was found in avahi 0.8-5.

Noroxi assessment

Priority: Monitor (action score 22/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.37% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: avahi (AlmaLinux:9) 0.8-15.el9; avahi-compat-howl (AlmaLinux:9) 0.8-15.el9; avahi-compat-howl-devel (AlmaLinux:9) 0.8-15.el9.

Low priority for now. Upgrade to avahi (AlmaLinux:9) 0.8-15.el9; avahi-compat-howl (AlmaLinux:9) 0.8-15.el9; avahi-compat-howl-devel (AlmaLinux:9) 0.8-15.el9 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

MediumCVSS 5.5 · v3.1—No exploit Fix available
Published
May 7, 2021
Updated
Jun 17, 2026
EPSS
0.3% · 31th percentile

Report tools

JSON

Action score

22

Monitor

Low priority for now.

CVSS
22 / 40 · 5.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.3%

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-3502

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
avahiavahi

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • avahi avahi0.8-5

Versions reported by the vendor

Affected version ranges reported by the assigning authority (redhat). Independent of NVD's CPE analysis and usually ahead of it.

  • n/a avahi

    • 0.8-5affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:9avahibefore 0.8-15.el90.8-15.el9
AlmaLinux:9avahi-compat-howlbefore 0.8-15.el90.8-15.el9
AlmaLinux:9avahi-compat-howl-develbefore 0.8-15.el90.8-15.el9
AlmaLinux:9avahi-compat-libdns_sdbefore 0.8-15.el90.8-15.el9
AlmaLinux:9avahi-compat-libdns_sd-develbefore 0.8-15.el90.8-15.el9
AlmaLinux:9avahi-develbefore 0.8-15.el90.8-15.el9
AlmaLinux:9avahi-glibbefore 0.8-15.el90.8-15.el9
AlmaLinux:9avahi-glib-develbefore 0.8-15.el90.8-15.el9
AlmaLinux:9avahi-libsbefore 0.8-15.el90.8-15.el9
AlmaLinux:9avahi-toolsbefore 0.8-15.el90.8-15.el9
Alpine:v3.18avahibefore 0.8-r50.8-r5
Debian:12avahibefore 0.8-60.8-6
openSUSE:Tumbleweedavahibefore 0.8-7.20.8-7.2
Red Hat:enterprise_linux:9::appstreamavahi-autoipd-debuginfobefore 0:0.8-15.el90:0.8-15.el9
Red Hat:enterprise_linux:9::appstreamavahi-compat-howl-debuginfobefore 0:0.8-15.el90:0.8-15.el9
Red Hat:enterprise_linux:9::appstreamavahi-compat-libdns_sd-debuginfobefore 0:0.8-15.el90:0.8-15.el9
Red Hat:enterprise_linux:9::appstreamavahi-debuginfobefore 0:0.8-15.el90:0.8-15.el9
Red Hat:enterprise_linux:9::appstreamavahi-debugsourcebefore 0:0.8-15.el90:0.8-15.el9
Red Hat:enterprise_linux:9::appstreamavahi-dnsconfd-debuginfobefore 0:0.8-15.el90:0.8-15.el9
Red Hat:enterprise_linux:9::appstreamavahi-glibbefore 0:0.8-15.el90:0.8-15.el9
Red Hat:enterprise_linux:9::appstreamavahi-glib-debuginfobefore 0:0.8-15.el90:0.8-15.el9
Red Hat:enterprise_linux:9::appstreamavahi-gobject-debuginfobefore 0:0.8-15.el90:0.8-15.el9
Red Hat:enterprise_linux:9::appstreamavahi-libs-debuginfobefore 0:0.8-15.el90:0.8-15.el9
Red Hat:enterprise_linux:9::appstreamavahi-toolsbefore 0:0.8-15.el90:0.8-15.el9

+12

Same product

avahi: all records

Other highest-scoring records for the same primary product.

  • CVE-2008-5081The originates_from_local_legacy_unicast_socket function (avahi-core/server.c) in avahi-daemon in Avahi before 0.6.24 allows remote attacker
    40Plan
  • CVE-2017-6519avahi-daemon in Avahi through 0.6.32 and 0.7 inadvertently responds to IPv6 unicast queries with source addresses that are not on-link, whic
    37Monitor
  • CVE-2021-26720avahi-daemon-check-dns.sh in the Debian avahi package through 0.8-4 is executed as root via /etc/network/if-up.d/avahi-daemon, and allows a
    31Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2010-2244Jul 8, 2010 · The AvahiDnsPacket function in avahi-core/socket.c in avahi-daemon in Avahi 0.6.16 and 0.6.25 allows remote attackers to cause a denial of s
    18Monitor
  • ← EarlierCVE-2011-1002Feb 22, 2011 · avahi-core/socket.c in avahi-daemon in Avahi before 0.6.29 allows remote attackers to cause a denial of service (infinite loop) via an empty
    29Monitor
  • Later →CVE-2021-3468Jun 2, 2021 · A flaw was found in avahi in versions 0.6 up to 0.8.
    22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
almalinux:avahi0.8-15.el9 · AlmaLinux:9Package registry (OSV)
almalinux:avahi-compat-howl0.8-15.el9 · AlmaLinux:9Package registry (OSV)
almalinux:avahi-compat-howl-devel0.8-15.el9 · AlmaLinux:9Package registry (OSV)
almalinux:avahi-compat-libdns_sd0.8-15.el9 · AlmaLinux:9Package registry (OSV)
almalinux:avahi-compat-libdns_sd-devel0.8-15.el9 · AlmaLinux:9Package registry (OSV)
almalinux:avahi-devel0.8-15.el9 · AlmaLinux:9Package registry (OSV)
almalinux:avahi-glib0.8-15.el9 · AlmaLinux:9Package registry (OSV)
almalinux:avahi-glib-devel0.8-15.el9 · AlmaLinux:9Package registry (OSV)
almalinux:avahi-libs0.8-15.el9 · AlmaLinux:9Package registry (OSV)
almalinux:avahi-tools0.8-15.el9 · AlmaLinux:9Package registry (OSV)
alpine:avahi0.8-r5 · Alpine:v3.18Package registry (OSV)
debian:avahi0.8-6 · Debian:12Package registry (OSV)
opensuse:avahi0.8-7.2 · openSUSE:TumbleweedPackage registry (OSV)
red hat:avahi-autoipd-debuginfo0:0.8-15.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:avahi-compat-howl-debuginfo0:0.8-15.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:avahi-compat-libdns_sd-debuginfo0:0.8-15.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:avahi-debuginfo0:0.8-15.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:avahi-debugsource0:0.8-15.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:avahi-dnsconfd-debuginfo0:0.8-15.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:avahi-glib0:0.8-15.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:avahi-glib-debuginfo0:0.8-15.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:avahi-gobject-debuginfo0:0.8-15.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:avahi-libs-debuginfo0:0.8-15.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:avahi-tools0:0.8-15.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:avahi-tools-debuginfo0:0.8-15.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-617 · Reachable Assertion

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

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