CVE-2023-20135

Code execution via ISO verification race

Published Sep 13, 2023 · Updated Dec 16, 2025

Improper ISO image verification in Cisco IOS XR Software allows local users to execute arbitrary code on the underlying operating system. Concurrent ISO installation and install-query operations separate verification from use, allowing a modified image to win the race. Exploitation requires authenticated local access, control of the ISO image, and parallel install requests; successful exploitation compromises device code integrity.

CVSS severity5.7
Medium
EPSS probability0.09%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper ISO image verification in Cisco IOS XR Software allows local users to execute arbitrary code on the underlying operating system. Concurrent ISO installation and install-query operations separate verification from use, allowing a modified image to win the race. Exploitation requires authenticated local access, control of the ISO image, and parallel install requests; successful exploitation compromises device code integrity.

The record

CVE
CVE-2023-20135
Published
Sep 13, 2023
Updated
Dec 16, 2025
Vendor
ClamAV
Product
Cisco IOS XR Software
Classifications
CWE-347, CWE-367, T1068
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Sep 13, 2023CVE publishedPublication date reported by the CVE source.
  2. Dec 16, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=7.5.2
  2. Affected versionversion=7.5.3
  3. Affected versionversion=7.5.4
  4. Affected versionversion=7.7.1
  5. Affected versionversion=7.7.2
  6. Affected versionversion=7.7.21
  7. Affected versionversion=7.8.1
  8. Affected versionversion=7.8.2
  9. Affected versionversion=7.9.1
  10. Affected versionversion=7.9.2

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

ClamAV · Cisco IOS XR Softwareversion=7.5.2; version=7.5.3; version=7.5.4; version=7.7.1; version=7.7.2; version=7.7.21; version=7.8.1; version=7.8.2; version=7.9.1; version=7.9.2

Published CVSS scores

5.7CiscoCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:N/E:X/RL:X/RC:X

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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
CWE-367Time-of-check Time-of-use (TOCTOU) Race Condition
T1068Exploitation for Privilege Escalation

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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