CVE-2021-1539Network attack vector

Authenticated restricted-command execution via TACACS bypass

Published Jun 4, 2021 · Updated Nov 7, 2024

Authorization bypass in Cisco ASR 5000 Series Software allows remote authenticated users to execute restricted CLI commands over SSH. StarOS incorrectly authorizes non-interactive CLI commands submitted in crafted SSH requests, bypassing TACACS command restrictions. A valid account and network access to SSH are required; successful exploitation exposes only a subset of CLI commands, with confidentiality and availability impacts reported.

CVSS severity8.1
High
EPSS probability1.09%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authorization bypass in Cisco ASR 5000 Series Software allows remote authenticated users to execute restricted CLI commands over SSH. StarOS incorrectly authorizes non-interactive CLI commands submitted in crafted SSH requests, bypassing TACACS command restrictions. A valid account and network access to SSH are required; successful exploitation exposes only a subset of CLI commands, with confidentiality and availability impacts reported.

The record

CVE
CVE-2021-1539
Published
Jun 4, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco ASR 5000 Series Software
Classifications
CWE-863, T1059.008
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 4, 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 vectornetwork
Required privilegesauthenticated

What is affected?

ClamAV · Cisco ASR 5000 Series Softwareversion=n/a

Published CVSS scores

8.1CiscoCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
6.5NIST NVDAV:N/AC:L/Au:S/C:P/I:P/A:P
8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-863Incorrect Authorization
T1059.008Command and Scripting Interpreter: Network Device CLI

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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