CVE-2025-20241VulnerabilityPublished 27 Aug 2025

CVE-2025-20241: Cisco NX-OS Software · Compiler Optimization Removal or Modification of Security-critical Code

Affects Cisco NX-OS SoftwareSource CVE Database V5

Not known to be exploited · CVSS 7.4 High.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

7.4High

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 20% 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:C/C:N/I:N/A:H

Attack Vector: Adjacent
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: 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: 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 27 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 2026-10-25.

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 NX-OS Software	Affected =9.2 =9.3 =10.1 =10.2 =10.3 =10.4 =10.5	Fixed in–

AI-suggested

European organizations should implement a multi-layered mitigation strategy: 1) Immediate patching: Apply Cisco's security updates for NX-OS as soon as they become available, prioritizing affected versions in production. 2) Network segmentation: Restrict Layer 2 adjacency to critical network devices by segmenting management and routing infrastructure using VLANs, private VLANs, or VRFs to limit exposure. 3) Access control: Enforce strict control over devices allowed on the same Layer 2 domain as vulnerable switches, including port security, 802.1X authentication, and MAC address filtering. 4) Monitoring and detection: Deploy network monitoring tools to detect anomalous IS-IS packets or unexpected IS-IS process restarts and device reloads. 5) Incident response readiness: Prepare playbooks for rapid response to DoS events affecting routing infrastructure, including fallback routing plans and device recovery procedures. 6) Vendor coordination: Engage with Cisco support for guidance and to obtain patches or workarounds. 7) Network design review: Consider alternative routing protocols or redundant paths to minimize single points of failure. 8) Limit administrative access and ensure secure management interfaces to reduce risk of lateral movement enabling Layer 2 adjacency exploitation.

Description

A vulnerability in the Intermediate System-to-Intermediate System (IS-IS) feature of Cisco NX-OS Software for Cisco Nexus 3000 Series Switches and Cisco Nexus 9000 Series Switches in standalone NX-OS mode could allow an unauthenticated, adjacent attacker to cause the IS-IS process to unexpectedly restart, which could cause an affected device to reload. This vulnerability is due to insufficient input validation when parsing an ingress IS-IS packet. An attacker could exploit this vulnerability by sending a crafted IS-IS packet to an affected device. A successful exploit could allow the attacker to cause the unexpected restart of the IS-IS process, which could cause the affected device to reload, resulting in a denial of service (DoS) condition. Note: The IS-IS protocol is a routing protocol. To exploit this vulnerability, an attacker must be Layer 2-adjacent to the affected device.

Impact

For European organizations, this vulnerability poses a significant risk to network availability and operational continuity. Cisco Nexus 3000 and 9000 Series switches are widely deployed in data centers, enterprise core networks, and service provider environments across Europe. An attacker exploiting this vulnerability could cause network outages by forcing device reloads, disrupting routing and connectivity. This could impact critical infrastructure sectors such as finance, telecommunications, government, healthcare, and energy, where network uptime is essential. The requirement for Layer 2 adjacency limits the attack surface to local network segments or compromised devices within the same broadcast domain, but insider threats or lateral movement by attackers could facilitate exploitation. Disruption of IS-IS routing could also affect large-scale enterprise and carrier networks that rely on this protocol for dynamic routing, potentially causing widespread service degradation or outages. The high availability demands and regulatory requirements in Europe for critical infrastructure heighten the impact severity. Additionally, the cascading effect of device reloads could complicate incident response and recovery efforts, increasing downtime and operational costs.

References

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-n39k-isis-dos-JhJA8Rfx (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 27 Aug 2025, 16:48 UTC

Technical details

References

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