CVE-2021-31755
CRITICALCISA KEVEPSS 100th pctlDescription
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.
How to fix
Actively exploited, no published fix found yet
CISA required action: Apply updates per vendor instructions.
Federal remediation due: 2021-11-17
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Exploit Intelligence
Very high risk: more likely to be exploited than 100% of all known CVEs.
Tenda AC11 Router Stack Buffer Overflow Vulnerability
Tenda AC11 devices contain a stack buffer overflow vulnerability in /goform/setmac which allows attackers to execute code via a crafted post request.
Apply updates per vendor instructions.
Remediation due: 2021-11-17
References
Related Vulnerabilities
Other CWE-787 (Out-of-bounds Write) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2025-22457 | Critical | 9.0 | 100% | KEV + Ransom | Fix |
| CVE-2025-0282 | Critical | 9.0 | 100% | KEV + Ransom | - |
| CVE-2015-3113 | Critical | 9.8 | 100% | KEV | Fix |
| CVE-2021-20038 | Critical | 9.8 | 100% | KEV + Ransom | - |
| CVE-2023-4863 | High | 8.8 | 100% | KEV | Fix |
| CVE-2020-16040 | Medium | 6.5 | 100% | - | Fix |
Common questions
How do I fix CVE-2021-31755?
No published fix for CVE-2021-31755 has been found yet. It is on the CISA Known Exploited Vulnerabilities list; federal agencies must remediate by 2021-11-17. Apply the vendor's mitigations per CISA's guidance.
Is CVE-2021-31755 being actively exploited?
Yes. CVE-2021-31755 is listed in the CISA Known Exploited Vulnerabilities catalog, which means exploitation has been observed in the wild. US federal agencies were required to remediate it by 2021-11-17. Treat it as a priority whatever its CVSS score says.
How severe is CVE-2021-31755?
CVE-2021-31755 has a CVSS v3 base score of 9.8, rated critical. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-11-10.