CVE-2021-34708

Arbitrary code execution via unverified ISO script

Published Sep 9, 2021 · Updated Nov 7, 2024

Improper image verification in Cisco IOS XR Software allows local users to execute arbitrary code through a modified installation ISO. An unsigned script inside the ISO is not verified while an installation request is processed, so modified script content is trusted and executed. Exploitation requires administrator installation rights or delivery of the altered image to an administrator who uses it for an upgrade.

CVSS severity6.0
Medium
EPSS probability0.18%
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 allows local users to execute arbitrary code through a modified installation ISO. An unsigned script inside the ISO is not verified while an installation request is processed, so modified script content is trusted and executed. Exploitation requires administrator installation rights or delivery of the altered image to an administrator who uses it for an upgrade.

The record

CVE
CVE-2021-34708
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

7.2NIST NVDAV:L/AC:L/Au:N/C:C/I:C/A:C
6.7NIST NVDCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
6.0CiscoCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N

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.

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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