dbcve.org
Ios XrOperating system · Cisco

CVE-2023-20191

HIGH · 7.5 CVSS v3.1 Published 2023-09-13
Fix available
A fix is available. Upgrade to 7.7.21 / 7.9.2 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A vulnerability in the access control list (ACL) processing on MPLS interfaces in the ingress direction of Cisco IOS XR Software could allow an unauthenticated, remote attacker to bypass a configured ACL. This vulnerability is due to incomplete support for this feature. An attacker could exploit this vulnerability by attempting to send traffic through an affected device. A successful exploit could allow the attacker to bypass an ACL on the affected device. There are workarounds that address this vulnerability. This advisory is part of the September 2023 release of the Cisco IOS XR Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: September 2023 Semiannual Cisco IOS XR Software Security Advisory Bundled Publication .

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A vulnerability in Cisco IOS XR Software allows unauthenticated remote attackers to bypass configured ACLs on MPLS interfaces in the ingress direction due to incomplete ACL processing support for this feature. Attackers can exploit this by sending traffic through affected devices, effectively circumventing security policies intended to filter that traffic.

MitigationApply Cisco's published workarounds or install the corresponding software patch from the September 2023 security advisory; verify ACL enforcement on MPLS interfaces after implementation.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Ios XrOperating system
Affected:< 7.7.21>= 7.8, < 7.9.2= 7.10

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the device operating system
    Run 'show version' or 'show inventory' to confirm the device runs Cisco IOS XR Software
    Affected if The device is not running Cisco IOS XR (this CVE only applies to IOS XR)
  2. Determine the IOS XR version
    Execute 'show version' and locate the IOS XR release number in the output
    Affected if The version is < 7.7.21, OR >= 7.8 and < 7.9.2, OR exactly 7.10
  3. Verify MPLS is enabled on the device
    Run 'show mpls interfaces' or 'show mpls ldp neighbor' to check if MPLS is configured on any interfaces
    Affected if MPLS is enabled on one or more interfaces (the vulnerability only affects MPLS interfaces)
  4. Inspect ACL configurations on MPLS interfaces
    Run 'show access-lists' combined with 'show running-config interface' for MPLS-enabled interfaces to identify ingress ACL bindings
    Affected if Ingress ACLs are applied to MPLS interfaces (the bypass only matters where ACLs are meant to filter traffic)

A user is affected if they run Cisco IOS XR in any of the listed vulnerable versions AND have MPLS interfaces with ingress ACLs configured, because the vulnerability allows traffic to bypass those ACLs.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 7.7.21 / 7.9.2 or later
Fixed in 7.7.217.9.2
Interim mitigation

Apply Cisco's published workarounds or install the corresponding software patch from the September 2023 security advisory; verify ACL enforcement on MPLS interfaces after implementation.

Recommended fix High confidence

Upgrade to IOS XR 7.7.21 or later (for 7.7.x branch), or 7.9.2 or later (for 7.8.x/7.9.x branch); 7.10.x requires waiting for subsequent fix

  1. 1. Identify the current Cisco IOS XR Software version using 'show version' command
  2. 2. Determine which version branch your current software is on (7.7.x, 7.8.x, 7.9.x, or 7.10.x)
  3. 3. For versions < 7.7.21: Upgrade to IOS XR 7.7.21 or later in the 7.7.x train
  4. 4. For versions >= 7.8.x and < 7.9.2: Upgrade to IOS XR 7.9.2 or later in the 7.9.x train
  5. 5. For version 7.10.x: Monitor Cisco.com for the fixed release or applicable patch
  6. 6. After upgrade, verify that ACLs are being applied correctly on MPLS interfaces using 'show access-lists' and interface configuration checks
  7. 7. Test that ACL bypass is no longer possible by verifying traffic is being filtered as expected
Caveat Standard IOS XR upgrade considerations apply - review release notes for any configuration or feature changes between versions

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Ios Xr Scoped from the published advisory
  • Consultation4.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,480
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-20191 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data