VulnerabilityPublished 4 Mar 2026

CVE-2026-20103: Cisco Secure Firewall Adaptive Security Appliance (ASA) Software · Unthrottled Resource Allocation

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

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Not known to be exploited · CVSS 8.6 High.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score

8.6High

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

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

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
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: 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: 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 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 9.12.4.48 – 9.23.1.3 97 affected builds	Fixed in–
CiscoCisco Secure Firewall Threat Defense (FTD) Software	Affected 6.4.0.16 – 7.7.10.1 47 affected builds	Fixed in–

AI-suggested

Organizations should immediately identify all Cisco ASA and FTD devices running affected software versions and prioritize upgrading to fixed versions once Cisco releases patches. Until patches are available, implement network-level mitigations such as rate limiting and filtering of SSL VPN traffic to restrict the volume of incoming connections and malformed packets. Deploy intrusion prevention systems (IPS) with signatures targeting anomalous SSL VPN traffic patterns. Monitor VPN server logs and network traffic for unusual spikes or malformed packet activity indicative of exploitation attempts. Restrict access to the SSL VPN service to trusted IP ranges where feasible, reducing exposure to unauthenticated attackers. Regularly review and harden VPN configurations, disable unused services, and apply Cisco's security advisories and best practices. Maintain an incident response plan to quickly restore VPN availability in case of an attack. Engage with Cisco support for guidance and updates on patch availability. Consider deploying redundant VPN gateways to maintain remote access availability during potential attacks.

Description

A vulnerability in the Remote Access SSL VPN functionality of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to exhaust device memory resulting in a denial of service (DoS) condition to new Remote Access SSL VPN connections. This does not affect the management interface, though it may become temporarily unresponsive. This vulnerability is due to trusting user input without validation. An attacker could exploit this vulnerability by sending crafted packets to the Remote Access SSL VPN server. A successful exploit could allow the attacker to cause the device web interface to stop responding, resulting in a DoS condition.

Impact

The primary impact of CVE-2026-20103 is a denial of service condition that disrupts remote access VPN connectivity, which can severely affect organizations relying on Cisco ASA and FTD devices for secure remote access. This can lead to operational downtime, loss of productivity, and potential inability for remote employees or partners to access corporate resources. Although the management interface is not directly affected, the temporary unresponsiveness of the web interface complicates incident response and recovery efforts. In critical infrastructure, government, financial, healthcare, and large enterprise environments where Cisco ASA/FTD devices are widely deployed, such a disruption can have cascading effects on business continuity and security posture. The vulnerability does not allow data theft or modification but compromises availability, which is a key security pillar. The ease of exploitation (no authentication or user interaction required) and network accessibility of the vulnerable service increase the risk of widespread attacks if exploited. Organizations without timely patching or mitigations may face targeted DoS attacks, especially during geopolitical tensions or cyber conflict scenarios.

References

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-vpn-m9sx6MbC (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 11 Mar 2026, 20:07 UTC

Technical details

References

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