CVE-2026-20074
Published: 11 March 2026
Summary
CVE-2026-20074 is a high-severity Improper Validation of Specified Type of Input (CWE-1287) vulnerability in Cisco IOS XR (inferred from references). Its CVSS base score is 7.4 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 15.9th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SC-5 (Denial-of-service Protection) and SI-10 (Information Input Validation).
Deeper analysis
CVE-2026-20074 is a vulnerability in the Intermediate System-to-Intermediate System (IS-IS) multi-instance routing feature of Cisco IOS XR Software. It stems from insufficient input validation of ingress IS-IS packets, which could allow an unauthenticated, adjacent attacker to cause the IS-IS process to restart unexpectedly. The vulnerability affects devices running this software where the IS-IS protocol is enabled, and it has a CVSS v3.1 base score of 7.4 (AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H), associated with CWE-1287.
An attacker must be Layer 2-adjacent to the affected device and form an IS-IS adjacency before exploiting the issue by sending crafted IS-IS packets. A successful exploit would restart the IS-IS process, leading to a temporary loss of connectivity to advertised networks and resulting in a denial-of-service (DoS) condition on the device.
Cisco has published a security advisory detailing the vulnerability, affected releases, and mitigation options, available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-isis-dos-kDMxpSzK.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-11219
Vulnerability details
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Crafted IS-IS packets exploit input validation flaw to crash routing process, directly enabling application/system exploitation for DoS (T1499.004).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly requires validation of ingress IS-IS packets, addressing the root cause of insufficient input validation that leads to process restart.
Explicitly protects against crafted-packet DoS conditions that cause loss of routing process and network connectivity.
Enforces boundary filtering and flow controls on Layer-2-adjacent IS-IS traffic before adjacency formation or malicious packets reach the routing process.