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CVE Record

CVE-2021-34727: Cisco IOS XE SD-WAN Software Buffer Overflow Vulnerability

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.

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

CVE-2021-34727 is a critical Cisco IOS XE SD-WAN flaw that can be triggered remotely without authentication. If exploited, it could let an attacker crash an affected device or possibly run commands with root-level privileges, creating both outage and device-compromise risk.

Executive priority

Treat this as a high-priority infrastructure risk. The worst case is root-level device compromise; the lower-case outcome is service disruption from device reloads. Confirm exposure quickly and remediate according to Cisco guidance.

Technical view

The issue is a CWE-120 buffer overflow in the vDaemon process. Cisco describes insufficient bounds checking while processing traffic. Crafted traffic to an affected device may cause memory corruption, arbitrary root-level command execution, or a reload denial of service. CVSS 3.1 is 9.8 with network attack vector and no privileges required.

Likely exposure

Exposure is limited to environments running Cisco IOS XE SD-WAN Software on affected devices. The supplied source bundle does not provide affected release ranges or CPEs, so teams must confirm versions against Cisco's advisory and their inventory.

Exploitation context

The source bundle supports remote unauthenticated exploitability and high impact. It does not state public exploitation, and the CVE is not marked as CISA KEV in the provided data. Treat internet or untrusted-network reachability as higher urgency, but do not assume active exploitation from these sources alone.

Researcher notes

Useful evidence is strong on vulnerability class, attack preconditions, and impact, but incomplete on affected version ranges and fixes in the supplied bundle. Avoid assuming exploit availability or active exploitation without additional cited evidence.

Mitigation direction

  • Review Cisco's advisory for affected releases and fixed-release guidance.
  • Prioritize remediation for exposed Cisco IOS XE SD-WAN devices.
  • Reduce untrusted network reachability to affected devices where operationally possible.
  • Monitor affected devices for unexpected reloads or compromise indicators.

Validation and detection

  • Inventory Cisco IOS XE SD-WAN devices and software versions.
  • Compare each device version against Cisco's advisory.
  • Identify devices reachable from untrusted or external networks.
  • Review device history for unexpected reloads or abnormal behavior.
Prepared
Confidence
high
Sources
3

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-120: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2021-34727 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
2Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.8CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

9.8Critical
CVSS 3.1 vector shape for CVE-2021-34727Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
CiscoCisco IOS XE SD-WAN Softwaren/aListed
Weakness

CWE details

CWE-120

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-120 · source CWE mapping

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs