CVE-2021-34696Network attack vector

Unauthenticated ACL bypass via incorrect hardware programming

Published Sep 23, 2021 · Updated Nov 7, 2024

Improper access control in Cisco IOS XE Software on affected ASR 900 and ASR 920 routers allows remote attackers to bypass IPv4 ACLs. Hardware is programmed incorrectly when an ACL is installed through a method other than the configuration CLI, allowing prohibited transit traffic to pass. Exposure requires a vulnerable IOS XE release, supported ASR hardware, and an IPv4 ACL created outside the CLI; Cisco reports no mechanism for inspecting whether that ACL was programmed correctly.

CVSS severity5.8
Medium
EPSS probability1.00%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper access control in Cisco IOS XE Software on affected ASR 900 and ASR 920 routers allows remote attackers to bypass IPv4 ACLs. Hardware is programmed incorrectly when an ACL is installed through a method other than the configuration CLI, allowing prohibited transit traffic to pass. Exposure requires a vulnerable IOS XE release, supported ASR hardware, and an IPv4 ACL created outside the CLI; Cisco reports no mechanism for inspecting whether that ACL was programmed correctly.

The record

CVE
CVE-2021-34696
Published
Sep 23, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco IOS XE Software
Classifications
CWE-284
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 23, 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 privilegesunauthenticated

What is affected?

ClamAV · Cisco IOS XE Softwareversion=n/a

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:N
5.8Cisco Systems, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-284Improper Access Control

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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