CVE-2025-20217VulnerabilityPublished 14 Aug 2025

CVE-2025-20217: Cisco Firepower Threat Defense Software · Infinite Loop

Affects Cisco Firepower Threat Defense SoftwareSource CVE Database V5

Not known to be exploited · CVSS 8.6 High.

Data as of 26 Oct 2026, 08:30 UTC

CVSS 3.1 base score

8.6High

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

EPSS: 0.7% chance of exploitation in 30 days – higher than 53% 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 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 Firepower Threat Defense Software	Affected =7.1.0 =7.1.0.1 =7.2.0 =7.1.0.2 =7.2.0.1 =7.2.1 =7.3.0 =7.2.2 =7.2.3 =7.3.1 =7.1.0.3 =7.2.4 =7.2.5 =7.2.4.1 =7.3.1.1 =7.4.0 =7.2.5.1 =7.4.1 =7.2.6 =7.4.1.1 =7.2.7 =7.2.5.2 =7.3.1.2 =7.2.8 =7.6.0 =7.4.2 =7.2.8.1 =7.4.2.1 =7.2.9	Fixed in–

AI-suggested

1. Immediate deployment of Cisco's security patches or software updates addressing CVE-2025-20217 once available is the most effective mitigation. Organizations should prioritize upgrading affected FTD versions to patched releases. 2. In the interim, implement network-level filtering to block or rate-limit suspicious or anomalous traffic patterns that could trigger the infinite loop, based on traffic inspection logs and known attack signatures. 3. Monitor firewall and Snort process health closely using Cisco monitoring tools and system logs to detect repeated restarts or performance degradation indicative of exploitation attempts. 4. Employ network segmentation to isolate critical assets behind additional layers of security, reducing the blast radius if the firewall is temporarily impaired. 5. Engage in threat hunting and anomaly detection to identify potential exploitation attempts early. 6. Coordinate with Cisco support and subscribe to security advisories for timely updates and guidance. 7. Review and harden firewall configurations to minimize exposure of management interfaces and restrict access to trusted sources only. 8. Consider deploying complementary intrusion detection/prevention systems to provide redundancy in traffic inspection capabilities during remediation.

Description

A vulnerability in the packet inspection functionality of the Snort 3 Detection Engine of Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to incorrect processing of traffic that is inspected by an affected device. An attacker could exploit this vulnerability by sending crafted traffic through the affected device. A successful exploit could allow the attacker to cause the affected device to enter an infinite loop while inspecting traffic, resulting in a DoS condition. The system watchdog will restart the Snort process automatically.

Impact

For European organizations, this vulnerability poses a substantial risk to network security infrastructure stability and availability. Cisco FTD devices are widely deployed across enterprises, service providers, and critical infrastructure sectors in Europe for firewalling and intrusion prevention. An attacker exploiting this flaw could cause repeated denial of service conditions, leading to temporary loss of traffic inspection and potential blind spots in threat detection. This could facilitate further attacks or data exfiltration attempts going unnoticed. Organizations in sectors with stringent regulatory requirements for network security and uptime, such as finance, healthcare, energy, and government, could face operational disruptions and compliance challenges. Additionally, the automatic restart of the Snort process may not fully mitigate the risk if exploitation is continuous, potentially causing cascading failures or degraded firewall performance. Given the remote, unauthenticated nature of the exploit, attackers from anywhere could target European networks, increasing the threat landscape. The lack of confidentiality or integrity impact reduces the risk of data compromise directly from this vulnerability, but the availability impact alone is critical for maintaining secure and reliable network operations.

References

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

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 14 Aug 2025, 17:18 UTC

Technical details

References

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