Ios XrOperating system · Cisco
CVE-2021-34721
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 the CLI of Cisco IOS XR Software could allow an authenticated, local attacker to gain access to the underlying root shell of an affected device and execute arbitrary commands with root privileges. 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 confidenceMultiple vulnerabilities in the Cisco IOS XR Software CLI allow an authenticated local attacker to escape the restricted CLI shell and gain access to the underlying root shell, enabling execution of arbitrary commands with root privileges.
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
< 7.3.2>= 7.4.0, <= 7.4.1>= 7.4.0, < 7.4.1CVSS 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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Determine the IOS XR software versionExecute the command 'show version' or 'admin show version' on the device console or via SSH. Locate the version string (for example: Version 7.3.1 or Version 7.4.1).Affected if The displayed version falls outside the safe ranges: version is below 7.3.2, or falls between 7.4.0 and 7.4.1 inclusive.
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Identify if local authentication is configuredReview the device configuration using 'show running-config | include username' or 'show running-config | include aaa' to list locally configured user accounts and AAA settings.Affected if Local user accounts exist in the configuration (username commands present) or local authentication is enabled, as this allows the authenticated attacker to log in.
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Verify if console or terminal access is availableCheck the control plane configuration with 'show line' or 'show terminal' to confirm active console/Telnet/SSH sessions are permitted.Affected if Console, Telnet, or SSH access is enabled and reachable, providing a path for a local attacker to authenticate.
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Confirm the restricted shell is in useLog in with a non-root administrative account and observe whether you are placed in a restricted CLI shell (the XR EXEC mode) rather than a full root shell.Affected if The device uses the restricted CLI shell, as the vulnerability specifically allows escaping this shell to reach the root shell.
You are affected if your Cisco IOS XR version matches the vulnerable ranges (< 7.3.2 or 7.4.0 through 7.4.1) AND the device permits local console or SSH authentication to an account that would use the restricted CLI shell.
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 data7.3.27.4.1
Apply Cisco security updates/patches for IOS XR Software; restrict physical and console access to authorized personnel; implement least-privilege admin account policies.
Fix this in Ios Xr
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,600.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-34721 — 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-2021-34721 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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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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