Routing disruption via malformed IS-IS packets
Published Mar 11, 2026 · Updated Mar 11, 2026
Denial of service in Cisco IOS XR Software allows attackers to restart the IS-IS process by sending crafted ingress IS-IS packets. The multi-instance routing feature accepts malformed ingress IS-IS packet fields instead of rejecting them, causing the routing process to restart. Exploitation requires Layer 2 adjacency, a formed IS-IS adjacency, and multi-instance routing enabled; the restart temporarily disrupts connectivity to advertised networks.
Summary
What happened
Denial of service in Cisco IOS XR Software allows attackers to restart the IS-IS process by sending crafted ingress IS-IS packets. The multi-instance routing feature accepts malformed ingress IS-IS packet fields instead of rejecting them, causing the routing process to restart. Exploitation requires Layer 2 adjacency, a formed IS-IS adjacency, and multi-instance routing enabled; the restart temporarily disrupts connectivity to advertised networks.
The record
- CVE
- CVE-2026-20074
- Published
- Mar 11, 2026
- Updated
- Mar 11, 2026
- Vendor
- ClamAV
- Product
- Cisco IOS XR Software
- Classifications
- CWE-1287, T1499.004
- Attack vector
- adjacent
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 11, 2026CVE publishedPublication date reported by the CVE source.
- Mar 11, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=24.1.1
- Affected versionversion=24.1.2
- Affected versionversion=24.2.1
- Affected versionversion=24.2.11
- Affected versionversion=24.2.2
- Affected versionversion=24.2.20
- Affected versionversion=24.2.21
- Affected versionversion=24.3.1
- Affected versionversion=24.3.2
- Affected versionversion=24.3.20
- Affected versionversion=24.3.30
- Affected versionversion=24.4.1
- Affected versionversion=24.4.10
- Affected versionversion=24.4.15
- Affected versionversion=24.4.2
- Affected versionversion=24.4.30
- Affected versionversion=25.1.1
- Affected versionversion=25.1.2
- Affected versionversion=25.2.1
- Affected versionversion=25.2.15
- Affected versionversion=7.10.1
- Affected versionversion=7.10.2
- Affected versionversion=7.11.1
- Affected versionversion=7.11.2
- Affected versionversion=7.11.21
- Affected versionversion=7.8.1
- Affected versionversion=7.8.2
- Affected versionversion=7.8.22
- Affected versionversion=7.8.23
- Affected versionversion=7.9.1
- Affected versionversion=7.9.2
- Affected versionversion=7.9.21
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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