Security Resilience

CVE-2020-3566

DoS in Cisco Ios Xr 6.4.2

CISA KEVActive ExploitationEUVD ExploitedDoS
Published
29 August 2020
Modified
28 October 2025
KEV Added
03 November 2021
Patch / advisory
CVSS Score v3.1 8.6
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
EPSS Score 0.037 90th percentile
Risk Priority 88 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2020-3566 is a high-severity Uncontrolled Resource Consumption (CWE-400) vulnerability in Cisco Ios Xr. Its CVSS base score is 8.6 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique OS Exhaustion Flood (T1499.001); ranked in the top 10% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

A vulnerability in the Distance Vector Multicast Routing Protocol (DVMRP) feature of Cisco IOS XR Software allows an unauthenticated remote attacker to exhaust process memory on an affected device. The issue stems from insufficient queue management for Internet Group Management Protocol (IGMP) packets and is tracked under CWE-400 and CWE-770. Successful exploitation can destabilize other processes, including interior and exterior routing protocols. The flaw carries a CVSS 3.1 score of 8.6 with network attack vector, no required privileges or user interaction, and changed scope affecting availability.

An attacker can trigger the condition simply by sending crafted IGMP traffic to a reachable device running the vulnerable software. No authentication or local access is needed, enabling remote exploitation over the network that leads to memory exhaustion and potential denial of service against routing functions.

Cisco has published software updates to address the vulnerability in the associated security advisory. The flaw also appears in CISA's catalog of known exploited vulnerabilities, indicating confirmed in-the-wild activity.

EU & UK References

Vulnerability Data

A vulnerability in the Distance Vector Multicast Routing Protocol (DVMRP) feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to exhaust process memory of an affected device. The vulnerability is due to insufficient queue management for Internet…

more

Group Management Protocol (IGMP) packets. An attacker could exploit this vulnerability by sending crafted IGMP traffic to an affected device. A successful exploit could allow the attacker to cause memory exhaustion, resulting in instability of other processes. These processes may include, but are not limited to, interior and exterior routing protocols. Cisco will release software updates that address this vulnerability.

CWE(s)
KEV Date Added
03 November 2021

Related Threats

MITRE ATT&CK Enterprise Techniques

T1499.001 OS Exhaustion Flood Impact
Adversaries may launch a denial of service (DoS) attack targeting an endpoint's operating system (OS).
T1499.002 Service Exhaustion Flood Impact
Adversaries may target the different network services provided by systems to conduct a denial of service (DoS).
T1499.003 Application Exhaustion Flood Impact
Adversaries may target resource intensive features of applications to cause a denial of service (DoS), denying availability to those applications.
T1001.003 Protocol or Service Impersonation Command And Control
Adversaries may impersonate legitimate protocols or web service traffic to disguise command and control activity and thwart analysis efforts.
T1003 OS Credential Dumping Credential Access
Adversaries may attempt to dump credentials to obtain account login and credential material, normally in the form of a hash or a clear text password.
T1005 Data from Local System Collection
Adversaries may search local system sources, such as file systems, configuration files, local databases, virtual machine files, or process memory, to find files of interest and sensitive data prior to Exfiltration.
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2020-3569Same product: Cisco Asr 9001both on KEV
CVE-2023-20155Same vendor: Cisco
CVE-2023-20047Same vendor: Cisco
CVE-2024-20526Same vendor: Cisco
CVE-2024-20321Same vendor: Cisco
CVE-2025-20209Same product: Cisco Ios Xr
CVE-2020-3118Same product: Cisco Asr 9001both on KEV
CVE-2024-20327Same product: Cisco Asr 9001
CVE-2023-20049Same product: Cisco Asr 9001
CVE-2025-20141Same product: Cisco Ios Xr

Affected Assets

cisco
ios xr
6.4.2

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

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Detect
Catch it (NIST detect / respond)

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Harden
Shrink the surface (DISA STIG)
  • 5 hardening rules · 3 OS baselines
Validate
Prove the fix (OWASP ASVS)

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Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

addresses: CWE-400 CWE-770

Limiting concurrent sessions directly prevents uncontrolled resource consumption by capping the number of active sessions per user or account.

addresses: CWE-400 CWE-770

Contingency plan testing includes resource exhaustion scenarios to verify recovery, making it harder for attackers to sustain exploits that cause uncontrolled consumption.

addresses: CWE-400 CWE-770

Updated contingency plans include current procedures to detect, contain, and recover from resource exhaustion, limiting an attacker's ability to sustain impact from uncontrolled consumption.

addresses: CWE-400 CWE-770

Alternate site allows resumption of operations if resource exhaustion at the primary site is exploited to cause unavailability.

addresses: CWE-400 CWE-770

Alternate telecommunications services enable resumption of essential functions when primary services become unavailable due to uncontrolled resource consumption.

addresses: CWE-400 CWE-770

Planning and coordination of security activities (scans, tests, maintenance) directly imposes scheduling and throttling that prevents those activities from producing uncontrolled resource consumption.

addresses: CWE-400 CWE-770

Performance metrics and monitoring inherently track resource consumption patterns, making uncontrolled consumption easier to detect and mitigate.

addresses: CWE-400 CWE-770

Terminating idle connections bounds resource consumption that would otherwise allow uncontrolled accumulation of open sessions.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.IR-04 partial match
blocks

Monitoring capacity and taking action to maintain availability directly reduces unchecked resource allocation.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

removes
removes
removes
removes
finds

Pre-agreed severity-based prioritization and resource allocation during incident triage reduce the likelihood that an attacker-induced resource exhaustion will overwhelm the organization before corrective action is taken.

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (higher-evidence rows only; rows rated `none` are excluded).

Oracle Linux 8 (2 rules)
  • V-248552 OL 8 must be configured so that all network connections associated with SSH traffic terminate after becoming unresponsive. blocks CWE-770
  • V-248553 OL 8 must be configured so that all network connections associated with SSH traffic are terminated after 10 minutes of becoming unresponsive. blocks CWE-770
Oracle Linux 9 (2 rules)
  • V-271710 OL 9 must be configured so that all network connections associated with SSH traffic are terminated after 10 minutes of becoming unresponsive. blocks CWE-770
  • V-271709 OL 9 must be configured so that all network connections associated with SSH traffic terminate after becoming unresponsive. blocks CWE-770
RHEL 8 (1 rule)
  • V-230244 RHEL 8 must be configured so that all network connections associated with SSH traffic terminate after becoming unresponsive. blocks CWE-770

References