PatchSiren

PatchSiren cyber security CVE debrief

CVE-2020-3566 Cisco CVE debrief

CVE-2020-3566 is a Cisco IOS XR Software DVMRP memory exhaustion vulnerability that CISA has listed in the Known Exploited Vulnerabilities catalog. For defenders, the key takeaway is simple: this issue has been publicly identified as known exploited, so IOS XR environments should be reviewed and updated using Cisco’s guidance as soon as possible.

Vendor
Cisco
Product
IOS XR
CVSS
Unknown
CISA KEV
Listed
Original CVE published
2021-11-03
Original CVE updated
2021-11-03
Advisory published
2021-11-03
Advisory updated
2021-11-03

Who should care

Cisco IOS XR administrators, network security teams, and incident responders responsible for perimeter and core routing infrastructure should prioritize this CVE, especially any environment running DVMRP-related functionality.

Technical summary

The official records in this corpus identify the issue as a memory exhaustion vulnerability in Cisco IOS XR Software’s DVMRP handling. CISA’s KEV entry confirms the vulnerability is known exploited and directs organizations to apply updates per vendor instructions. No additional impact details are included in the supplied source corpus, so validation should rely on the official Cisco and NVD/CVE records linked here.

Defensive priority

High. CISA lists CVE-2020-3566 in KEV, which makes it a priority for patching and exposure review in Cisco IOS XR deployments.

Recommended defensive actions

  • Check whether any Cisco IOS XR systems use DVMRP-related functionality or are otherwise exposed to the affected code path.
  • Review the Cisco advisory and related vendor update guidance referenced by the official records.
  • Apply Cisco-provided updates or mitigations as directed by the vendor.
  • Verify remediation across all IOS XR assets rather than a single device or site.
  • Monitor Cisco IOS XR systems for unusual resource exhaustion or instability until remediation is complete.

Evidence notes

This debrief is based only on the supplied official corpus: the CISA KEV source item, the CVE.org record link, and the NVD detail link. The corpus confirms the vulnerability name, product, KEV status, date added (2021-11-03), and due date (2022-05-03). It does not provide version ranges, exploit mechanics, or broader impact details, so those are intentionally not inferred here.

Official resources

CISA KEV lists this vulnerability as known exploited and provides a remediation deadline of 2022-05-03. The CVE and KEV metadata in this corpus are dated 2021-11-03; no newer timing information is provided here.