CVE-2019-1918: Cisco IOS XR Software Intermediate System–to–Intermediate System Denial of Service Vulnerability

Severity: high (CVSS 7.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2019-08-07 · updated 2026-06-17
Weakness: CWE-20

Description

A vulnerability in the implementation of Intermediate System–to–Intermediate System (IS–IS) routing protocol functionality in Cisco IOS XR Software could allow an unauthenticated attacker who is in the same IS-IS area to cause a denial of service (DoS) condition. The vulnerability is due to incorrect processing of IS–IS link-state protocol data units (PDUs). An attacker could exploit this vulnerability by sending specific link-state PDUs to an affected system to be processed. A successful exploit could allow the attacker to cause incorrect calculations used in the weighted remote shared risk link groups (SRLG) or in the IGP Flexible Algorithm. It could also cause tracebacks to the logs or potentially cause the receiving device to crash the IS–IS process, resulting in a DoS condition.

Affected products

Cisco Carrier Routing System: 6.5.1, 6.5.3
Cisco IOS XR Software: from 6.5.2 before 6.6.3 — fixed in 6.6.3

How to fix

Upgrade to a fixed version: Cisco IOS XR Software 6.6.3. Check the vendor advisory for mitigations.

References

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