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NVD / CVE Program· CNA mitre

CVE-2021-26720: avahi-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

Noroxi assessment

Priority: Monitor (action score 31/100)

  • 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: 0.39% (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 (Debian:12) 0.8-4; avahi (Debian:9) 0.6.32-2+deb9u1; avahi (openSUSE:Leap 15.2) 0.7-lp152.3.6.1.

Low priority for now. Upgrade to avahi (Debian:12) 0.8-4; avahi (Debian:9) 0.6.32-2+deb9u1; avahi (openSUSE:Leap 15.2) 0.7-lp152.3.6.1 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

avahi-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 local attacker to cause a denial of service or create arbitrary empty files via a symlink attack on files under /run/avahi-daemon. NOTE: this only affects the packaging for Debian GNU/Linux (used indirectly by SUSE), not the upstream Avahi product.

HighCVSS 7.8 · v3.1—No exploit Fix available
Published
Feb 17, 2021
Updated
Jun 16, 2026
EPSS
0.3% · 33th percentile

Report tools

JSON

Action score

31

Monitor

Low priority for now.

CVSS
31 / 40 · 7.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.3%

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

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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
debiandebian linux

Affected versions

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

  • avahi avahiup to 0.8-4 inclusive
  • debian debian linux10.0
  • debian debian linux9.0

Package-level exposure

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

EcosystemPackageAffected rangeFix
Debian:12avahibefore 0.8-40.8-4
Debian:9avahibefore 0.6.32-2+deb9u10.6.32-2+deb9u1
openSUSE:Leap 15.2avahibefore 0.7-lp152.3.6.10.7-lp152.3.6.1
openSUSE:Leap 15.2avahi-glib2before 0.7-lp152.3.6.10.7-lp152.3.6.1
openSUSE:Leap 15.2avahi-monobefore 0.7-lp152.3.6.10.7-lp152.3.6.1
openSUSE:Leap 15.2avahi-qt4before 0.7-lp152.3.6.10.7-lp152.3.6.1
openSUSE:Leap 15.3avahibefore 0.6.32-5.13.10.6.32-5.13.1
openSUSE:Leap 15.3avahi-glib2before 0.6.32-5.13.10.6.32-5.13.1
openSUSE:Tumbleweedavahibefore 0.8-7.20.8-7.2
SUSE:Linux Enterprise High Performance Computing 15-ESPOSavahibefore 0.6.32-5.13.10.6.32-5.13.1
SUSE:Linux Enterprise High Performance Computing 15-ESPOSavahi-glib2before 0.6.32-5.13.10.6.32-5.13.1
SUSE:Linux Enterprise Module for Basesystem 15 SP2avahibefore 0.7-3.6.10.7-3.6.1
SUSE:Linux Enterprise Module for Basesystem 15 SP2avahi-glib2before 0.7-3.6.10.7-3.6.1
SUSE:Linux Enterprise Software Development Kit 12 SP5avahibefore 0.6.32-32.12.20.6.32-32.12.2
SUSE:Linux Enterprise Software Development Kit 12 SP5avahi-glib2before 0.6.32-32.12.30.6.32-32.12.3

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-2011-1002avahi-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

Published before and after this one in the same product

  • ← EarlierCVE-2007-3372Jun 22, 2007 · The Avahi daemon in Avahi before 0.6.20 allows attackers to cause a denial of service (exit) via empty TXT data over D-Bus, which triggers a
    8Monitor
  • ← 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
  • Later →CVE-2021-3502May 7, 2021 · A flaw was found in avahi 0.8-5.
    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
alpine:avahi0 · Alpine:v3.10Package registry (OSV)
debian:avahi0.8-4 · Debian:12Package registry (OSV)
opensuse:avahi0.7-lp152.3.6.1 · openSUSE:Leap 15.2Package registry (OSV)
opensuse:avahi-glib20.7-lp152.3.6.1 · openSUSE:Leap 15.2Package registry (OSV)
opensuse:avahi-mono0.7-lp152.3.6.1 · openSUSE:Leap 15.2Package registry (OSV)
opensuse:avahi-qt40.7-lp152.3.6.1 · openSUSE:Leap 15.2Package registry (OSV)
suse:avahi0.7-3.6.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP2Package registry (OSV)
suse:avahi-glib20.7-3.6.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP2Package 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
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-59 · Improper Link Resolution Before File Access ('Link Following')

CVSS vector

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

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (9 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records