What is CVE-2021-31756?

CVE-2021-31756 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-2021-31756?

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

Is CVE-2021-31756 known to be exploited?

3 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Buffer overflow in Tenda Ac11

CVE-2021-31756

An issue was discovered on Tenda AC11 devices with firmware through 02.03.01.104_CN. A stack buffer overflow vulnerability in /gofrom/setwanType allows attackers to execute arbitrary code on the system via a crafted post request. This occurs when input vector controlled by malicious attack get copied to the stack variable.

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: 0.029 (86.4th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 86th percentile — 86.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.029 · newest: 0.029 · change: 0.000

Affected products

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

Public proof-of-concept exploits

References

github.com/Yu3H0/IoT_CVE/tree/main/Tenda/CVE_1 (Exploit, Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2021-31756?: CVE-2021-31756 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-2021-31756?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2021-31756 known to be exploited?: 3 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.