What is CVE-2021-31755?

CVE-2021-31755 is a critical-severity vulnerability in Tenda Ac11, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2021-05-07.

How severe is CVE-2021-31755?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2021-31755 known to be exploited?

Yes. CVE-2021-31755 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 9 public proof-of-concept repositories are indexed.

Buffer overflow in Tenda Ac11

CVE-2021-31755

An issue was discovered on Tenda AC11 devices with firmware through 02.03.01.104_CN. A stack buffer overflow vulnerability in /goform/setmac allows attackers to execute arbitrary code on the system via a crafted post request.

Vulnerability class: Buffer Overflow

Published 2021-05-07 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.865 (99.7th percentile), scored 2026-10-19.

High probability of exploitation in the next 30 days — patch promptly. 100th percentile — 99.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.869 · newest: 0.865 · change: -0.004

Affected products

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

CISA KEV (Known Exploited Vulnerabilities)

This CVE is on the CISA KEV catalog, added on 2021-11-03. CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.

BOD 22-01 due date: 2021-11-17.

Required action: Apply updates per vendor instructions.

Public proof-of-concept exploits

References

github.com/Yu3H0/IoT_CVE/tree/main/Tenda/CVE_3 (Exploit, Third Party Advisory, Issue Tracking, Broken Link)
134c704f-9b21-4f2e-91b3-4a467353bcc0 (US Government Resource)

Frequently asked questions

What is CVE-2021-31755?: CVE-2021-31755 is a critical-severity vulnerability in Tenda Ac11, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2021-05-07.
How severe is CVE-2021-31755?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2021-31755 known to be exploited?: Yes. CVE-2021-31755 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 9 public proof-of-concept repositories are indexed.