dbcve.org
Ios XrOperating system · Cisco

CVE-2021-1243

HIGH · 7.5 CVSS v3.1 Published 2021-02-04
Fix available
A fix is available. Upgrade to 6.6.4 / 7.0.2 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 Local Packet Transport Services (LPTS) programming of the SNMP with the management plane protection feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to allow connections despite the management plane protection that is configured to deny access to the SNMP server of an affected device. This vulnerability is due to incorrect LPTS programming when using SNMP with management plane protection. An attacker could exploit this vulnerability by connecting to an affected device using SNMP. A successful exploit could allow the attacker to connect to the device on the configured SNMP ports. Valid credentials are required to execute any of the SNMP requests.

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's Local Packet Transport Services (LPTS) programming allows SNMP connections to bypass management plane protection that was configured to deny SNMP server access. The issue stems from incorrect LPTS programming when SNMP is used with management plane protection. While valid SNMP credentials are required to execute requests, the vulnerability allows the initial connection to succeed despite the protection policy.

MitigationApply the Cisco IOS XR Software update that addresses the LPTS programming flaw. Verify that management plane protection rules are correctly blocking unauthorized SNMP access after the update.

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:> 6.1.1, < 6.6.4>= 7.0.0, < 7.0.2= 6.7.1= 7.0.11= 7.1.0= 7.2.0

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 Cisco IOS XR version
    Run 'show version' on the device and locate the software version string (e.g., 6.7.1, 7.0.11, 7.2.0)
    Affected if The installed version matches any of these: greater than 6.1.1 and less than 6.6.4; greater than or equal to 7.0.0 and less than 7.0.2; equal to 6.7.1, 7.0.11, 7.1.0, or 7.2.0
  2. Verify SNMP is configured
    Run 'show snmp' and check if SNMP is enabled or any SNMP configuration lines appear in the running config (look for 'snmp-server' commands)
    Affected if SNMP is actively configured on the device (any snmp-server settings present)
  3. Confirm management plane protection is configured
    Run 'show management-plane protection' or inspect the running configuration for 'management-plane protection' or 'mpls management-plane' entries
    Affected if Management plane protection is configured on the device
  4. Check the applied LPTS entries for SNMP
    Run 'show lpts bindings' or 'show lpts pfilter brief' and examine the LPTS entries for the SNMP port (UDP 161) to see if connections are being permitted or dropped
    Affected if SNMP traffic is permitted in LPTS despite management plane protection being configured to deny it (entries show permit instead of drop for SNMP)

The device is affected if it runs a vulnerable IOS XR version, has SNMP configured, and management plane protection rules are not properly blocking SNMP access as intended.

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.

From vendor data
Upgrade available Upgrade to 6.6.4 / 7.0.2 or later
Fixed in 6.6.47.0.2
Interim mitigation

Apply the Cisco IOS XR Software update that addresses the LPTS programming flaw. Verify that management plane protection rules are correctly blocking unauthorized SNMP access after the update.

Fix this in Ios Xr Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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Scan for this in your stack

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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-2021-1243 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