CVE-2021-34713

Line-card reboot via Layer 2 punt spin loop

Published Sep 9, 2021 · Updated Nov 7, 2024

A denial-of-service flaw in Cisco IOS XR Software for ASR 9000 routers allows unauthenticated adjacent attackers to reboot line cards. The Layer 2 punt code mishandles specific Ethernet frames and enters a spin loop that makes network processors unresponsive. An attacker must share the affected network segment; successful exploitation interrupts service by rebooting the targeted line card.

CVSS severity7.4
High
EPSS probability0.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A denial-of-service flaw in Cisco IOS XR Software for ASR 9000 routers allows unauthenticated adjacent attackers to reboot line cards. The Layer 2 punt code mishandles specific Ethernet frames and enters a spin loop that makes network processors unresponsive. An attacker must share the affected network segment; successful exploitation interrupts service by rebooting the targeted line card.

The record

CVE
CVE-2021-34713
Published
Sep 9, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco IOS XR Software
Classifications
CWE-399, T1499
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 9, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 7, 2024Record 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.

  1. Affected versionversion=n/a

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco IOS XR Softwareversion=n/a

Published CVSS scores

7.4Cisco PSIRTCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-399Resource Exhaustion
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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