CVE-2021-34709

Arbitrary code execution via certificate validation race

Published Sep 9, 2021 · Updated Nov 7, 2024

Improper image verification in Cisco IOS XR Software on affected 8000 and NCS 540 routers allows local users to execute arbitrary code. During an install request, a race condition lets another authenticated administrator replace the certificate used to determine whether the image certificate was issued by Cisco. Exploitation requires administrator access and winning the race while a modified ISO is installed, leading to code execution on the router OS.

CVSS severity6.0
Medium
EPSS probability0.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper image verification in Cisco IOS XR Software on affected 8000 and NCS 540 routers allows local users to execute arbitrary code. During an install request, a race condition lets another authenticated administrator replace the certificate used to determine whether the image certificate was issued by Cisco. Exploitation requires administrator access and winning the race while a modified ISO is installed, leading to code execution on the router OS.

The record

CVE
CVE-2021-34709
Published
Sep 9, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco IOS XR Software
Classifications
CWE-347, T1601.001
Attack vector
local
Privileges
admin

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 vectorlocal
Required privilegesadmin

What is affected?

ClamAV · Cisco IOS XR Softwareversion=n/a

Published CVSS scores

6.4NIST NVDCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
6.0Cisco Systems, Inc.CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N
6.9NIST NVDAV:L/AC:M/Au:N/C:C/I:C/A:C

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)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature
T1601.001Patch System Image

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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