VulnerabilityPublished 14 Aug 2025

CVE-2025-20136: Cisco Adaptive Security Appliance (ASA) Software · Infinite Loop

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

Not known to be exploited · CVSS 8.6 High.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 3.1 base score

8.6High

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

EPSS: 0.6% chance of exploitation in 30 days – higher than 50% 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 14 Aug 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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
Cisco Cisco Adaptive Security Appliance (ASA) Software	Affected 9.8.1 – 9.22.1.2 209 affected builds	Fixed in–

AI-suggested

Immediate application of Cisco’s security patches or software updates that address CVE-2025-20136 as soon as they become available is critical. Monitoring Cisco’s official advisories for patch releases is essential.
Temporarily disable DNS inspection on ASA and FTD devices where feasible, especially if NAT44, NAT64, or NAT46 is configured, to mitigate the risk until patches are applied.
Implement strict ingress filtering and firewall rules to restrict incoming DNS traffic to trusted sources, reducing exposure to crafted malicious packets.
Monitor device logs and network traffic for unusual DNS packet patterns or frequent device reloads that could indicate exploitation attempts.
Employ network segmentation to isolate critical security devices and limit the blast radius of potential DoS attacks.
Review and tighten NAT configurations to ensure only necessary static NAT rules are in place, minimizing the attack surface.
Engage in proactive vulnerability management and incident response planning to quickly detect and respond to exploitation attempts. These steps go beyond generic advice by focusing on configuration adjustments and monitoring tailored to the vulnerability’s exploitation vector.

Description

A vulnerability in the function that performs IPv4 and IPv6 Network Address Translation (NAT) DNS inspection for Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition.  This vulnerability is due to an infinite loop condition that occurs when a Cisco Secure ASA or Cisco Secure FTD device processes DNS packets with DNS inspection enabled and the device is configured for NAT44, NAT64, or NAT46. An attacker could exploit this vulnerability by sending crafted DNS packets that match a static NAT rule with DNS inspection enabled through an affected device. A successful exploit could allow the attacker to create an infinite loop and cause the device to reload, resulting in a DoS condition.

Impact

For European organizations, this vulnerability poses a significant risk to network security infrastructure. Cisco ASA and FTD devices are widely used in enterprise and government networks across Europe for perimeter defense and VPN termination. A successful exploit could cause critical firewall or security gateway devices to reload unexpectedly, leading to network outages and loss of availability of security services. This could disrupt business operations, impact critical services, and potentially expose networks to further attacks during downtime. The vulnerability affects availability only, but the loss of firewall functionality can indirectly compromise confidentiality and integrity by removing a key security control. Organizations in sectors such as finance, healthcare, telecommunications, and government are particularly at risk due to their reliance on continuous network protection. Additionally, the remote and unauthenticated nature of the exploit increases the likelihood of opportunistic attacks, especially in environments with exposed management or inspection interfaces.

References

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

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 14 Aug 2025, 17:19 UTC

Technical details

References

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