CVE-2021-27793

Login denial via intermittent TACACS+ authorization failure

Published Aug 12, 2021 · Updated Aug 3, 2024

TACACS+ authorization failure in Brocade Fabric OS after 8.2.0 and before 8.2.3a or after 9.0.0 and before 9.0.1b allows attackers to deny logins. Broadcom has not published the underlying implementation error that makes the TACACS+ authorization decision fail intermittently. Exposure requires AAA TACACS+ and a valid account for the affected user; the documented impact is intermittent switch-login denial only.

CVSS severity4.3
Medium
EPSS probability0.91%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

TACACS+ authorization failure in Brocade Fabric OS after 8.2.0 and before 8.2.3a or after 9.0.0 and before 9.0.1b allows attackers to deny logins. Broadcom has not published the underlying implementation error that makes the TACACS+ authorization decision fail intermittently. Exposure requires AAA TACACS+ and a valid account for the affected user; the documented impact is intermittent switch-login denial only.

The record

CVE
CVE-2021-27793
Published
Aug 12, 2021
Updated
Aug 3, 2024
Vendor
Brocade Communications Systems
Product
Brocade Fabric OS
Classifications
CWE-863, T1499
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 12, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=Versions before Brocade Fabric OS v9.0.1b and after 9.0.0, also before Brocade Fabric OS v8.2.3a and after v8.2.0

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Brocade Communications Systems · Brocade Fabric OSversion=Versions before Brocade Fabric OS v9.0.1b and after 9.0.0, also before Brocade Fabric OS v8.2.3a and after v8.2.0

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
4.3BroadcomCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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 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-863Incorrect Authorization
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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