How severe is CVE-2021-31755?

CVE-2021-31755 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-31755 being actively exploited?

Yes. CVE-2021-31755 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2021-11-03, which means active exploitation has been confirmed. It should be prioritised for remediation.

What products are affected by CVE-2021-31755?

CVE-2021-31755 affects Tenda Ac11 Firmware. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-31755?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.

Does CVE-2021-31755 have an EU (EUVD) identifier?

Yes. CVE-2021-31755 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-18639. It is also flagged as exploited in the EUVD (since 2021-11-03).

When was CVE-2021-31755 published?

CVE-2021-31755 was published on 2021-05-07 and last updated on 2026-06-17.

CVE-2021-31755

CVE-2021-31755 is a critical-severity vulnerability in Tenda Ac11 Firmware with a CVSS 3.x base score of 9.8. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2021-11-03). The underlying weakness is classified as CWE-787.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 10.0
EPSS exploit prediction: 86% (100th percentile)
Actively exploited: Yes — listed in CISA KEV (added 2021-11-03)
EU (EUVD) id: EUVD-2021-18639
EU exploitation: Flagged exploited in the ENISA EU Vulnerability Database (since 2021-11-03)
Weakness: CWE-787
Affected product: Tenda Ac11 Firmware
Published: 2021-05-07
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is 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.
How severe is CVE-2021-31755?: CVE-2021-31755 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-31755 being actively exploited?: Yes. CVE-2021-31755 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2021-11-03, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2021-31755?: CVE-2021-31755 affects Tenda Ac11 Firmware. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-31755?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2021-31755 have an EU (EUVD) identifier?: Yes. CVE-2021-31755 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-18639. It is also flagged as exploited in the EUVD (since 2021-11-03).
When was CVE-2021-31755 published?: CVE-2021-31755 was published on 2021-05-07 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:o:tenda:ac11_firmware:*:*:*:*:*:*:*:*

More vulnerabilities in Tenda Ac11 Firmware

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CVE-2021-46262 — Critical (CVSS 9.8): Tenda AC Series Router AC11_V02.03.01.104_CN was discovered to contain a stack buffer overflow in the PPPoE module.…
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