Ios XeOperating system · Cisco
CVE-2021-1398
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 · uneditedA vulnerability in the boot logic of Cisco IOS XE Software could allow an authenticated, local attacker with level 15 privileges or an unauthenticated attacker with physical access to execute arbitrary code on the underlying Linux operating system of an affected device. This vulnerability is due to incorrect validations of specific function arguments that are passed to the boot script. An attacker could exploit this vulnerability by tampering with a specific file, which an affected device would process during the initial boot process. On systems that are protected by the Unified Extensible Firmware Interface (UEFI) secure boot feature, a successful exploit could allow the attacker to execute unsigned code at boot time and bypass the image verification check in the secure boot process of the affected device.
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 confidenceThis vulnerability in Cisco IOS XE Software's boot logic allows execution of arbitrary code on the underlying Linux OS due to insufficient validation of function arguments passed to the boot script. An attacker can exploit this by tampering with a specific file processed during initial boot. On systems with UEFI secure boot enabled, successful exploitation bypasses image verification, allowing unsigned code execution at boot time.
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 XeOperating system
= 3.7.0bs= 3.7.0s= 3.7.0xas= 3.7.0xbs= 3.7.1as= 3.7.1s= 3.7.2s= 3.7.2ts= 3.7.3s= 3.7.4as= 3.7.4s= 3.7.5sCVSS 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
- Physical
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:P/AC:L/PR:N/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 installed IOS XE versionRun 'show version' command from privileged exec mode and locate the IOS XE release number in the outputAffected if The displayed version matches any of these: 3.7.0bs, 3.7.0s, 3.7.0xas, 3.7.0xbs, 3.7.1as, 3.7.1s, 3.7.2s, 3.7.2ts, 3.7.3s, 3.7.4as, 3.7.4s, or 3.7.5s
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Verify UEFI secure boot statusRun 'show secure-boot status' or check boot configuration via 'show boot' to determine if secure boot is enabled on the deviceAffected if Secure boot is disabled or not configured, as the vulnerability can bypass image verification when secure boot is active
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Confirm boot script integrityCompare the boot configuration and any boot scripts (such as those in bootflash: or nvram:) against known-good baselines or verify their checksums if a baseline existsAffected if Any boot-related file has been modified without authorization or shows unexpected changes in content
A device is affected if it runs any of the listed IOS XE versions AND the boot script or configuration file can be tampered with, especially when UEFI secure boot is not enabled.
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 dataApply the Cisco IOS XE software update when available. For systems with UEFI secure boot, ensure it remains enabled as a defense-in-depth measure. Restrict physical access to network infrastructure and limit privileged (level 15) administrative access.
Fix this in Ios Xe
Scoped from the published advisory
- Consultation4.0 h
- Implementation6.0 h
- Testing4.0 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 $4,544.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-1398 — 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-2021-1398 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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