dbcve.org
Ios Xe Sd WanOperating system · Cisco

CVE-2021-34727

CRITICAL · 9.8 CVSS v3.1 Published 2021-09-23
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
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 vDaemon process in Cisco IOS XE SD-WAN Software could allow an unauthenticated, remote attacker to cause a buffer overflow on an affected device. This vulnerability is due to insufficient bounds checking when an affected device processes traffic. An attacker could exploit this vulnerability by sending crafted traffic to the device. A successful exploit could allow the attacker to cause a buffer overflow and possibly execute arbitrary commands with root-level privileges, or cause the device to reload, which could result in a denial of service condition.

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 confidence

A buffer overflow vulnerability exists in the vDaemon process of Cisco IOS XE SD-WAN Software due to insufficient bounds checking when processing incoming traffic. An unauthenticated remote attacker can send specially crafted traffic to trigger the overflow, potentially achieving arbitrary command execution with root-level privileges or causing device reload (DoS).

MitigationApply the vendor-supplied patch for CVE-2021-34727 when available. If immediate patching is not feasible, restrict network access to affected devices and implement traffic filtering at network perimeter to block unauthorized traffic targeting the vDaemon service.

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 Xe Sd WanOperating system
Affected:all versions

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
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/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 checks

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

  1. Identify the software platform
    Run 'show version' or 'show sdwan version' command to confirm the device is running Cisco IOS XE SD-WAN software.
    Affected if The device runs any version of Cisco IOS XE with SD-WAN functionality.
  2. Confirm SD-WAN feature is enabled
    Run 'show sdwan system' or check for vDaemon process presence via 'show process cpu | include vDaemon' or 'show process memory | include vDaemon'.
    Affected if The vDaemon process is running on the device, indicating SD-WAN is active.
  3. Check device network exposure
    Review interface configurations and access lists to determine if the device's SD-WAN interfaces are reachable from untrusted networks. Use 'show ip interface brief' and 'show access-lists' to assess exposure.
    Affected if The SD-WAN management or data plane interfaces are exposed to untrusted/network-perimeter-facing networks without filtering.
  4. Verify IOS XE version
    Run 'show version' and note the full IOS XE version string (for example, 16.9.x, 16.10.x, 16.11.x, 17.x.x). Compare against Cisco's official release notes for fixed versions.
    Affected if The device runs any IOS XE SD-WAN version prior to the vendor-patched release.

If the device runs Cisco IOS XE SD-WAN software with the vDaemon process active, it is affected by this vulnerability regardless of version.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the vendor-supplied patch for CVE-2021-34727 when available. If immediate patching is not feasible, restrict network access to affected devices and implement traffic filtering at network perimeter to block unauthorized traffic targeting the vDaemon service.

Fix this in Ios Xe Sd Wan Scoped from the published advisory
  • Consultation8.0 h
  • Implementation16.0 h
  • Testing12.0 h
  • Review / QA8.0 h
44.0 hours of engineering $7,720
Get help mitigating

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 locally
dbcve dependency scanner

Check whether your project pulls in CVE-2021-34727 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2021-34727 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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