NVD / CVE Program· CNA cisco

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

Noroxi assessment

Priority: Plan (action score 40/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 2.6% (FIRST EPSS); higher than 85.6% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to CISA the attack is automatable: targets can be found by mass scanning.
According to the record, no fixed version is available yet.

Add it to your regular patch cycle. Update when a fix is released; follow the vendor's advisory.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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 9.8 · v3.1—No exploit No fix recorded

BDU:2021-05546

Published: Sep 22, 2021
Updated: Jun 16, 2026
EPSS: 2.6% · 85th percentile
CWE: CWE-120

Report tools

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Action score

Plan

Add it to your regular patch cycle.

CVSS: 39 / 40 · 9.8 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 1 / 30 · 2.6%

CISA SSVC decision

Exploitation: none
Automatable: yes
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 9.8
CNA · cisco: 9.8; agree

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
No fixed version yet

If any of these changes, we'll tell you in the daily email digest.

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
cisco	ios xe sd-wan	cpe:2.3:o:cisco:ios_xe_sd-wan
cisco	1000 integrated services router	cpe:2.3:h:cisco:1000_integrated_services_router
cisco	1100-4g\/6g integrated services router	cpe:2.3:h:cisco:1100-4g\/6g_integrated_services_router
cisco	1100-4p integrated services router	cpe:2.3:h:cisco:1100-4p_integrated_services_router
cisco	1100-8p integrated services router	cpe:2.3:h:cisco:1100-8p_integrated_services_router
cisco	1100 integrated services router	cpe:2.3:h:cisco:1100_integrated_services_router
cisco	1101-4p integrated services router	cpe:2.3:h:cisco:1101-4p_integrated_services_router
cisco	1101 integrated services router	cpe:2.3:h:cisco:1101_integrated_services_router
cisco	1109-2p integrated services router	cpe:2.3:h:cisco:1109-2p_integrated_services_router
cisco	1109-4p integrated services router	cpe:2.3:h:cisco:1109-4p_integrated_services_router
cisco	1109 integrated services router	cpe:2.3:h:cisco:1109_integrated_services_router
cisco	1111x-8p integrated services router	cpe:2.3:h:cisco:1111x-8p_integrated_services_router

and 37 more

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

cisco ios xe sd-wanall versions

Versions reported by the vendor

Affected version ranges reported by the assigning authority (cisco). Independent of NVD's CPE analysis and usually ahead of it.

Cisco Cisco IOS XE SD-WAN Software
- n/aaffected

Same product

cisco: all records

Other highest-scoring records for the same primary product.

CVE-2025-20352A vulnerability in the Simple Network Management Protocol (SNMP) subsystem of Cisco IOS Software and Cisco IOS XE Software could allow the fKEV
72This week
CVE-2021-1301Cisco SD-WAN Buffer Overflow Vulnerabilities
40Plan
CVE-2021-1300Cisco SD-WAN Buffer Overflow Vulnerabilities
40Plan

Published before and after this one in the same product

← EarlierCVE-2021-34724Sep 22, 2021 · Cisco IOS XE SD-WAN Software Privilege Escalation Vulnerability
24Monitor
← EarlierCVE-2021-34725Sep 22, 2021 · Cisco IOS XE SD-WAN Software Command Injection Vulnerability
26Monitor
Later →CVE-2023-20035Mar 23, 2023 · Cisco IOS XE SD-WAN Software Command Injection Vulnerability
31Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: high · data can be read
Integrity: high · data or configuration can be modified
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: High

Weakness class (CWE)

CWE-120 · Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

CVSS vector

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

nvd-primary

Root cause

When data is copied, the source length is not compared with the size of the destination buffer. Excess data overwrites adjacent memory.

The bug in code

The whole CWE-120 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1char buf[256];
2memcpy(buf, pkt->data, pkt->len);

Fixed

1char buf[256];
2if (pkt->len > sizeof(buf)) {
3  return -EINVAL;
4}
5memcpy(buf, pkt->data, pkt->len);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

—

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxesdwan-rbuffover-vE2OB6tp

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records