Ios XrOperating system · Cisco
CVE-2021-1136
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 · uneditedMultiple vulnerabilities in Cisco Network Convergence System (NCS) 540 Series Routers, only when running Cisco IOS XR NCS540L software images, and Cisco IOS XR Software for the Cisco 8000 Series Routers could allow an authenticated, local attacker to execute unsigned code during the boot process on an affected device. For more information about these vulnerabilities, see the Details section of this advisory.
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 · moderate confidenceThis vulnerability in Cisco NCS 540 Series Routers (NCS540L) and Cisco 8000 Series Routers running Cisco IOS XR software allows an authenticated, local attacker to execute unsigned code during the boot process, compromising the boot chain integrity.
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
< 7.0.12>= 7.1.0, < 7.2.1< 7.2.1CVSS 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
- Local
- Complexity
- Low
- Privileges
- High
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
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 checksWork through these to decide whether this CVE applies to you.
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Identify device modelRun 'show inventory' or 'show platform' command to retrieve the hardware model informationAffected if Model is NCS540L or Cisco 8000 Series routers (if different model, not affected)
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Check IOS XR software versionRun 'show version' command to display the installed Cisco IOS XR versionAffected if Version is displayed and can be compared against affected ranges
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Compare version against affected rangesCompare the installed version from 'show version' against: < 7.0.12 OR >= 7.1.0 AND < 7.2.1Affected if Version falls within < 7.0.12, or between 7.1.0 and 7.2.1 (excluding 7.2.1 and above)
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Verify physical/local access contextConfirm the device is accessible to untrusted local users or could be accessed physically by unauthorized individualsAffected if Device has any physical or local access by untrusted personnel (combined with vulnerable version, this enables the attack vector)
Device is affected if it is an NCS540L or Cisco 8000 Series router running a vulnerable IOS XR version (before 7.0.12, or 7.1.x through 7.2.0) and could be accessed by an authenticated local attacker.
Generated from the published advisory. Verify against your own configuration.
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 data7.0.127.2.1
Apply the vendor-supplied software updates/patches from Cisco to address the boot process vulnerability. Restrict physical and local access to affected devices to trusted personnel only.
Fix this in Ios Xr
Scoped from the published advisory
- Consultation8.0 h
- Implementation16.0 h
- Testing12.0 h
- Review / QA8.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $12,352.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-1136 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-1136 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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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.
- 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
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