NVD / CVE Program· CNA cisco

CVE-2021-40125: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software IKEv2 Site-to-Site VPN Denial of Service Vulnerability

MediumCVSS 6.5 · v3.1—No exploit No fix recorded

Noroxi assessment

Priority: Monitor (action score 26/100)

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: 1% (FIRST EPSS); higher than 63.9% of all records.
Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
According to the record, no fixed version is available yet.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

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 Internet Key Exchange Version 2 (IKEv2) implementation of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an authenticated, remote attacker to trigger a denial of service (DoS) condition on an affected device. This vulnerability is due to improper control of a resource. An attacker with the ability to spoof a trusted IKEv2 site-to-site VPN peer and in possession of valid IKEv2 credentials for that peer could exploit this vulnerability by sending malformed, authenticated IKEv2 messages to an affected device. A successful exploit could allow the attacker to trigger a reload of the device.

BDU:2021-05921

Published: Oct 27, 2021
Updated: Aug 11, 2026
EPSS: 1.0% · 63th percentile
CWE: CWE-416

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 26 / 40 · 6.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 1.0%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 6.5
CNA · cisco: 5.3; 1.2 point gap

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

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.

Is your version affected? Check it

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	secure firewall threat defense	cpe:2.3:a:cisco:secure_firewall_threat_defense
cisco	adaptive security appliance software	cpe:2.3:o:cisco:adaptive_security_appliance_software
cisco	asa 5512-x firmware	cpe:2.3:o:cisco:asa_5512-x_firmware
cisco	asa 5512-x	cpe:2.3:h:cisco:asa_5512-x
cisco	asa 5505 firmware	cpe:2.3:o:cisco:asa_5505_firmware
cisco	asa 5505	cpe:2.3:h:cisco:asa_5505
cisco	asa 5515-x firmware	cpe:2.3:o:cisco:asa_5515-x_firmware
cisco	asa 5515-x	cpe:2.3:h:cisco:asa_5515-x
cisco	asa 5525-x firmware	cpe:2.3:o:cisco:asa_5525-x_firmware
cisco	asa 5525-x	cpe:2.3:h:cisco:asa_5525-x
cisco	asa 5545-x firmware	cpe:2.3:o:cisco:asa_5545-x_firmware
cisco	asa 5545-x	cpe:2.3:h:cisco:asa_5545-x

and 6 more

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 Adaptive Security Appliance (ASA) Software
- n/aaffected

Affected versions · NVD (5)

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

cisco adaptive security appliance software9.8.0 and later · before 9.8.4.40
cisco adaptive security appliance software9.9.0 and later · before 9.12.4.30
cisco adaptive security appliance software9.14.0 and later · before 9.14.3.9
cisco adaptive security appliance software9.15.0 and later · before 9.15.1.17
cisco adaptive security appliance software9.16.0 and later · before 9.16.2

Same product

cisco: all records

Other highest-scoring records for the same primary product.

CVE-2020-3259Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Web Services Information Disclosure VulnerabilityKEV
81Now
CVE-2020-3580Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Web Services Interface Cross-Site Scripting…KEV
80Now
CVE-2020-3187Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Web Services Path Traversal Vulnerability
65This week

Published before and after this one in the same product

← EarlierCVE-2021-34792Oct 27, 2021 · Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Resource Exhaustion Denial of Service Vulnerability
30Monitor
← EarlierCVE-2021-34794Oct 27, 2021 · Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software SNMP Access Control Vulnerability
21Monitor
Later →CVE-2021-34704Jan 11, 2022 · Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Web Services Denial of Service Vulnerability
30Monitor

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.

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

TR-21-0876 · Oct 28, 2021(Cisco Güvenlik Zafiyeti)

All national notices →

Not on record for this CVE: EPSS history · patch commit or PR link · researcher credit · variant or chain candidate · public bounty program.

Technical details

Attack conditions

Anyone who can reach it over the internet 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: Network
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

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

nvd-primary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

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

Vulnerable

1free(dev->buf);
2/* ... another thread is still running ... */
3process(dev->buf);

Fixed

1lock(&dev->lock);
2free(dev->buf);
3dev->buf = NULL;
4unlock(&dev->lock);

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 (0)

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-asaftd-ikev2-dos-g4cmrr7C

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

All records