CVE-2023-20191Network attack vector

Unauthenticated ACL bypass via denied-packet forwarding

Published Sep 13, 2023 · Updated Aug 2, 2024

Access control bypass in Cisco IOS XR Software allows remote attackers to forward traffic denied by an ingress MPLS ACL. When an explicit-null or de-aggregation label is popped, the deny path punts the packet to generate an ICMP unreachable response but forwards the denied packet instead of dropping it. Exploitation requires an affected platform with MPLS packet filtering and an IPv4 or IPv6 ingress ACL, and can expose networks protected by that ACL.

CVSS severity5.8
Medium
EPSS probability0.60%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Access control bypass in Cisco IOS XR Software allows remote attackers to forward traffic denied by an ingress MPLS ACL. When an explicit-null or de-aggregation label is popped, the deny path punts the packet to generate an ICMP unreachable response but forwards the denied packet instead of dropping it. Exploitation requires an affected platform with MPLS packet filtering and an IPv4 or IPv6 ingress ACL, and can expose networks protected by that ACL.

The record

CVE
CVE-2023-20191
Published
Sep 13, 2023
Updated
Aug 2, 2024
Vendor
ClamAV
Product
Cisco IOS XR Software
Classifications
CWE-863, CWE-284, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 13, 2023CVE publishedPublication date reported by the CVE source.
  2. Aug 2, 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=6.4.1
  2. Affected versionversion=6.5.1
  3. Affected versionversion=6.5.2
  4. Affected versionversion=6.5.3
  5. Affected versionversion=6.6.2
  6. Affected versionversion=6.6.25
  7. Affected versionversion=6.6.3
  8. Affected versionversion=6.6.4
  9. Affected versionversion=7.0.1
  10. Affected versionversion=7.0.2
  11. Affected versionversion=7.1.1
  12. Affected versionversion=7.1.2
  13. Affected versionversion=7.2.1
  14. Affected versionversion=7.2.2
  15. Affected versionversion=7.3.1
  16. Affected versionversion=7.3.2
  17. Affected versionversion=7.3.3
  18. Affected versionversion=7.3.5
  19. Affected versionversion=7.4.1
  20. Affected versionversion=7.4.2
  21. Affected versionversion=7.5.1
  22. Affected versionversion=7.5.2
  23. Affected versionversion=7.5.3
  24. Affected versionversion=7.5.4
  25. Affected versionversion=7.6.1
  26. Affected versionversion=7.6.2
  27. Affected versionversion=7.7.1
  28. Affected versionversion=7.7.2
  29. Affected versionversion=7.8.1
  30. Affected versionversion=7.8.2
  31. Affected versionversion=7.9.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco IOS XR Softwareversion=6.4.1; version=6.5.1; version=6.5.2; version=6.5.3; version=6.6.2; version=6.6.25; version=6.6.3; version=6.6.4; version=7.0.1; version=7.0.2; version=7.1.1; version=7.1.2; version=7.2.1; version=7.2.2; version=7.3.1; version=7.3.2; version=7.3.3; version=7.3.5; version=7.4.1; version=7.4.2; version=7.5.1; version=7.5.2; version=7.5.3; version=7.5.4; version=7.6.1; version=7.6.2; version=7.7.1; version=7.7.2; version=7.8.1; version=7.8.2; version=7.9.1

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
5.8Cisco PSIRTCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-863Incorrect Authorization
CWE-284Improper Access Control
T1190Exploit Public-Facing Application

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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