What is CVE-2021-27705?

CVE-2021-27705 is a critical-severity vulnerability in Tenda G1, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.8/10. Published 2021-04-14.

How severe is CVE-2021-27705?

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

Buffer overflow in Tenda G1

CVE-2021-27705

Buffer Overflow in Tenda G1 and G3 routers with firmware v15.11.0.17(9502)_CN allows remote attackers to execute arbitrary code via a crafted action/"qosIndex "request. This occurs because the "formQOSRuleDel" function directly passes the parameter "qosIndex" to strcpy without limit.

Vulnerability class: Buffer Overflow

Published 2021-04-14 · 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 (86.6th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 87th percentile — 86.6% 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

Tenda G1
Tenda G1 Firmware — versions v15.11.0.17\(9502\)_cn, v15.11.0.17(9502)_cn
Tenda G3
Tenda G3 Firmware — versions v15.11.0.17\(9502\)_cn, v15.11.0.17(9502)_cn

Weakness classification (CWE)

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

References

hackmd.io/Zb7lfFaNR0ScpaTssECFbg (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2021-27705?: CVE-2021-27705 is a critical-severity vulnerability in Tenda G1, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.8/10. Published 2021-04-14.
How severe is CVE-2021-27705?: Critical severity. CVSS v3 base score is 9.8 out of 10.