NVD / CVE Program· CNA cisco

CVE-2021-1439: Cisco Aironet Access Points FlexConnect Multicast DNS Denial of Service Vulnerability

Noroxi assessment

Priority: Monitor (action score 29/100)

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: 0.40% (FIRST EPSS).
Someone on the same network segment can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to the record, no fixed version is available yet.

Low priority for now. Update when a fix is released; follow the vendor's advisory.

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 vulnerability in the multicast DNS (mDNS) gateway feature of Cisco Aironet Series Access Points Software could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to insufficient input validation of incoming mDNS traffic. An attacker could exploit this vulnerability by sending a crafted mDNS packet to an affected device through a wireless network that is configured in FlexConnect local switching mode or through a wired network on a configured mDNS VLAN. A successful exploit could allow the attacker to cause the access point (AP) to reboot, resulting in a DoS condition.

HighCVSS 7.4 · v3.1—No exploit No fix recorded

BDU:2021-01811

Published: Mar 24, 2021
Updated: Jun 16, 2026
EPSS: 0.4% · 34th percentile
CWE: CWE-120

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 29 / 40 · 7.4 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.4%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 7.4
CNA · cisco: 7.4; agree

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
No fixed version yet

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

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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.

Vendor	Product	CPE
cisco	aironet access point software	cpe:2.3:a:cisco:aironet_access_point_software
cisco	1100 integrated services router	cpe:2.3:h:cisco:1100_integrated_services_router
cisco	aironet 1540	cpe:2.3:h:cisco:aironet_1540
cisco	aironet 1560	cpe:2.3:h:cisco:aironet_1560
cisco	aironet 1800	cpe:2.3:h:cisco:aironet_1800
cisco	aironet 2800	cpe:2.3:h:cisco:aironet_2800
cisco	aironet 3800	cpe:2.3:h:cisco:aironet_3800
cisco	aironet 4800	cpe:2.3:h:cisco:aironet_4800
cisco	catalyst 9100	cpe:2.3:h:cisco:catalyst_9100
cisco	catalyst iw6300	cpe:2.3:h:cisco:catalyst_iw6300
cisco	esw6300	cpe:2.3:h:cisco:esw6300
cisco	catalyst 9800 firmware	cpe:2.3:o:cisco:catalyst_9800_firmware

and 1 more

Affected versions

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

cisco aironet access point softwareall versions
cisco catalyst 9800 firmware17.1 and later · before 17.3.3

Versions reported by the vendor

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

Cisco Cisco Aironet Access Point Software (IOS XE Controller)
- n/aaffected

Same product

cisco: all records

Other highest-scoring records for the same primary product.

CVE-2017-3831A vulnerability in the web-based GUI of Cisco Mobility Express 1800 Series Access Points could allow an unauthenticated, remote attacker to
41Plan
CVE-2018-0234A vulnerability in the implementation of Point-to-Point Tunneling Protocol (PPTP) functionality in Cisco Aironet 1810, 1830, and 1850 Series
35Monitor
CVE-2015-6367Cisco Aironet 1800 devices with software 8.1(131.0) allow remote attackers to cause a denial of service (CPU consumption) by improperly esta
32Monitor

Published before and after this one in the same product

← EarlierCVE-2018-0250May 2, 2018 · A vulnerability in Central Web Authentication (CWA) with FlexConnect Access Points (APs) for Cisco Aironet 1560, 1810, 1810w, 1815, 1830, 18
16Monitor
← EarlierCVE-2021-1437Mar 24, 2021 · Cisco Aironet Access Points FlexConnect Upgrade Information Disclosure Vulnerability
30Monitor
Later →CVE-2021-1449Mar 24, 2021 · Cisco Access Point Software Arbitrary Code Execution Vulnerability
26Monitor

Remediation

Which version to upgrade to

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

No fix version is recorded for this entry. Check the references for vendor advisories.

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 on the same network segment can trigger it.
No account or password is required.
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

Impact can extend beyond the vulnerable component (scope changes).

Attack vector: Adjacent
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Changed
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-120 · Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

CVSS vector

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

nvd-primary

Root cause

When data is copied, the source length is not compared with the size of the destination buffer. Excess data overwrites adjacent memory.

The bug in code

The whole CWE-120 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1char buf[256];
2memcpy(buf, pkt->data, pkt->len);

Fixed

1char buf[256];
2if (pkt->len > sizeof(buf)) {
3  return -EINVAL;
4}
5memcpy(buf, pkt->data, pkt->len);

Attack context

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

Attack patterns (CAPEC)

ATT&CK techniques

—

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-aironet-mdns-dos-E6KwYuMx

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

All records