CVE-2021-31755Known exploitationNetwork attack vector

Unauthenticated code execution via setmac stack overflow

Published May 7, 2021 · Updated Oct 21, 2025

Stack buffer overflow in the Tenda AC11 setmac handler through firmware 02.03.01.104_CN allows remote attackers to execute code. The /goform/setmac handler processes attacker-controlled POST data without enforcing the destination stack buffer's bounds. No authentication or user interaction is required, and successful memory corruption grants code execution with the router service's privileges.

CVSS severity9.8
Critical
EPSS probability86.51%
Next 30 days · Nov 1, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack buffer overflow in the Tenda AC11 setmac handler through firmware 02.03.01.104_CN allows remote attackers to execute code. The /goform/setmac handler processes attacker-controlled POST data without enforcing the destination stack buffer's bounds. No authentication or user interaction is required, and successful memory corruption grants code execution with the router service's privileges.

The record

CVE
CVE-2021-31755
Published
May 7, 2021
Updated
Oct 21, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Oct 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
10.0NIST NVDAV:N/AC:L/Au:N/C:C/I:C/A:C
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsShadowserver observations through Sep 28, 2026. Gaps indicate unavailable data.
Sep 22, 2026Sep 28, 2026
View daily counts
Reporting dayUnique IPs
Sep 22, 20268
Sep 23, 20262
Sep 24, 20268
Sep 25, 202611
Sep 26, 20263
Sep 27, 202613
Sep 28, 20267
Latest reporting daySep 28, 2026
Latest daily unique IPs7
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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