VulnerabilityPublished 4 Mar 2026

CVE-2026-20049: Cisco Secure Firewall Adaptive Security Appliance (ASA) Software · Incorrect Calculation of Buffer Size

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

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Not known to be exploited · CVSS 7.7 High.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score

7.7High

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 23% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Changed
Confidentiality: None
Integrity: None
Availability: High

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

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
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: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

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 30 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 9.12.4.7 – 9.23.1.3 131 affected builds	Fixed in–
CiscoCisco Secure Firewall Threat Defense (FTD) Software	Affected 6.4.0.10 – 7.7.10.1 65 affected builds	Fixed in–

AI-suggested

Organizations should prioritize patching affected Cisco ASA and FTD devices with the latest software updates provided by Cisco once available. Given the extensive list of affected versions, verifying device software versions and upgrading to non-vulnerable releases is critical. Until patches are applied, organizations should enforce strict access controls and monitoring on VPN authentication mechanisms to reduce the risk of credential compromise. Implementing multi-factor authentication (MFA) for VPN access can further mitigate the risk of unauthorized exploitation. Network segmentation and limiting VPN access to trusted users and devices can reduce exposure. Monitoring VPN traffic for unusual patterns or malformed GCM-encrypted IPsec packets may help detect attempted exploitation. Incident response plans should include procedures for rapid recovery from device reloads to minimize downtime. Regular backups of device configurations and high availability configurations can reduce operational impact. Cisco’s advisories and security bulletins should be closely followed for updates and additional mitigation guidance.

Description

A vulnerability in the processing of Galois/Counter Mode (GCM)-encrypted Internet Key Exchange version 2 (IKEv2) IPsec traffic of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to the allocation of an insufficiently sized block of memory. An attacker could exploit this vulnerability by sending crafted GCM-encrypted IPsec traffic to an affected device. A successful exploit could allow the attacker to cause an unexpected reload of the device, resulting in a DoS condition. To exploit this vulnerability, the attacker must have valid credentials to establish a VPN connection with the affected device.

Impact

The primary impact of CVE-2026-20049 is a denial of service condition on affected Cisco firewall devices, which can cause unexpected reloads and temporary loss of firewall functionality. For organizations worldwide, this can disrupt secure VPN connectivity, potentially cutting off remote access for employees and partners. This disruption can affect business operations, especially for organizations heavily dependent on Cisco ASA and FTD devices for perimeter security and VPN services. The requirement for valid credentials to exploit the vulnerability limits the attack surface to authenticated users, but insider threats or compromised credentials could be leveraged by attackers. The broad range of affected software versions means many organizations may be vulnerable if they have not applied patches or mitigations. The DoS condition could also be used as a diversion tactic in multi-stage attacks or to degrade security posture during critical periods. While no confidentiality or integrity impacts are reported, the availability impact alone can have significant operational and financial consequences.

References

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-esp-dos-uv7yD8P5 (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 11 Mar 2026, 20:14 UTC

Technical details

References

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