VulnerabilityPublished 11 Mar 2026

CVE-2026-20074: Cisco IOS XR Software · Improper Validation of Specified Type of Input

Affects Cisco IOS XR SoftwareSource CVE Database V5

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Not known to be exploited · CVSS 7.4 High.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score

7.4High

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

EPSS: 0.1% chance of exploitation in 30 days – higher than 4% 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 11 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 IOS XR Software	Affected 7.8.1 – 25.2.15 32 affected builds	Fixed in–

AI-suggested

To mitigate CVE-2026-20074, organizations should prioritize upgrading affected Cisco IOS XR devices to patched versions provided by Cisco as soon as they become available. Until patches are applied, network administrators should implement strict Layer 2 segmentation and access controls to limit adjacency formation to trusted devices only. Employing features such as port security, dynamic ARP inspection, and DHCP snooping can reduce the risk of unauthorized devices forming adjacencies. Monitoring IS-IS adjacency states and process stability can help detect anomalous behavior indicative of exploitation attempts. Additionally, consider deploying network intrusion detection systems (NIDS) capable of inspecting IS-IS traffic for malformed packets. Network operators should review and harden IS-IS configurations to minimize exposure, including disabling unused IS-IS instances or interfaces where possible. Coordination with Cisco support for guidance on interim workarounds and best practices is recommended. Finally, maintain updated incident response plans to quickly address potential DoS events impacting routing infrastructure.

Description

A vulnerability in the Intermediate System-to-Intermediate System (IS-IS) multi-instance routing feature of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to cause the IS-IS process to restart unexpectedly. This vulnerability is due to insufficient input validation of ingress IS-IS packets. An attacker could exploit this vulnerability by sending crafted IS-IS packets to an affected device after forming an adjacency. A successful exploit could allow the attacker to cause the IS-IS process to restart unexpectedly, resulting in a temporary loss of connectivity to advertised networks and 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 and must have formed an adjacency.  

Impact

The primary impact of this vulnerability is a denial of service condition caused by the unexpected restart of the IS-IS routing process on affected Cisco IOS XR devices. This leads to temporary loss of routing information and connectivity to networks advertised via IS-IS, potentially causing network outages or degraded performance. For organizations relying on IS-IS for core or edge routing, this can disrupt critical communications, impacting business operations, service delivery, and customer experience. Service providers and large enterprises using Cisco IOS XR in their backbone or data center networks are particularly at risk. The requirement for Layer 2 adjacency and adjacency formation limits the attack surface to local network segments, but insider threats or compromised devices within the same broadcast domain could exploit this vulnerability. The disruption could also affect network redundancy and failover mechanisms, increasing the risk of prolonged outages. Although no known exploits are currently active in the wild, the vulnerability's high severity and broad affected versions warrant immediate attention to prevent potential exploitation.

References

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

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 11 Mar 2026, 17:14 UTC

Technical details

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