VulnerabilityPublished 4 Mar 2026

CVE-2026-20021: Cisco Secure Firewall Adaptive Security Appliance (ASA) Software · Memory Leak

Affects Cisco Secure Firewall Adaptive Security Appliance (ASA) SoftwareSource CVE Database V5

Compare

Not known to be exploited · CVSS 4.3 Medium.

Data as of 29 Oct 2026, 19:04 UTC

CVSS 3.1 base score

4.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 10% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Adjacent
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Adjacent: The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 4 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
CiscoCisco Secure Firewall Adaptive Security Appliance (ASA) Software	Affected 9.12.1 – 9.23.1.22 163 affected builds	Fixed in–
CiscoCisco Secure Firewall Threat Defense (FTD) Software	Affected 6.4.0 – 7.7.10.1 76 affected builds	Fixed in–

AI-suggested

Apply Cisco's official patches or software updates addressing CVE-2026-20021 as soon as they become available to ensure the vulnerability is remediated at the source.
Restrict OSPF adjacency and authentication to trusted devices and network segments only, minimizing exposure to potentially malicious actors.
Implement strict network segmentation and access controls to limit adjacency to Cisco ASA/FTD devices, reducing the attack surface.
Monitor OSPF traffic for anomalies such as unusual packet rates or malformed packets that could indicate exploitation attempts.
Employ rate limiting or filtering on OSPF protocol traffic at network boundaries to mitigate potential flooding attacks.
Regularly audit and review firewall configurations to ensure only necessary OSPF adjacencies exist and that authentication mechanisms are robust.
Maintain comprehensive logging and alerting on firewall health and resource utilization to detect early signs of memory exhaustion or DoS conditions.
Consider deploying redundant firewall appliances or high availability configurations to minimize impact of potential DoS events.

Description

A vulnerability in the OSPF protocol of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, adjacent attacker to exhaust memory on an affected device, resulting in a denial of service (DoS) condition. This vulnerability is due to improperly validating input by the OSPF protocol when parsing packets. An attacker could exploit this vulnerability by by sending crafted OSPF packets to an affected device. A successful exploit could allow the attacker to exhaust memory on the affected device, resulting in a DoS condition.

Impact

The primary impact of CVE-2026-20021 is a denial of service condition caused by memory exhaustion on affected Cisco ASA and FTD devices. This can disrupt firewall operations, potentially leading to network outages or degraded security posture due to device unavailability. Organizations relying on these devices for perimeter defense, VPN termination, or internal segmentation could experience significant operational disruption. The requirement for an authenticated, adjacent attacker reduces the likelihood of widespread remote exploitation but does not eliminate risk within internal or partner networks. Attackers who gain access to trusted network segments could leverage this vulnerability to disrupt network security controls, potentially facilitating further attacks or data breaches. Given the widespread deployment of Cisco ASA and FTD devices globally, especially in enterprise, government, and service provider environments, the vulnerability poses a notable risk to critical infrastructure and sensitive networks. The memory exhaustion could also lead to device crashes requiring manual intervention, increasing operational costs and downtime.

References

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-ospf-ZH8PhbSW (opens in a new tab)

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 11 Mar 2026, 20:08 UTC

Technical details

References

Community reviews

Related threats