CVE-2021-31755 — Ac11 Firmware
CRITICALCVE-2021-31755 is a critical-severity (CVSS 9.8) Out-of-bounds Write vulnerability in tenda ac11 firmware. It is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) — treat it as actively exploited and patch now. No vendor fix is recorded yet; mitigation options are listed below.
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…
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2021-11-03. Federal agencies were required to remediate by 2021-11-17.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2021-31755.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-31755 by exploitation likelihood (EPSS) against impact (CVSS). In the shaded patch-first corner (EPSS 50%+, CVSS 7.0+).
Where this sits among everything scored
Of 395,249 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Counts from FIRST.org, log-scaled.
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.
Affected Products
ac11 firmwaretendaResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Vendor / applianceDetect
Inventory every tenda ac11 firmware deployment and check each version against the affected-products list above.
Remediation status
No patch has shipped for CVE-2021-31755 yet — track the tenda ac11 firmware advisory for a fixed release and apply the workarounds below in the meantime.
Mitigate without a patch
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.
How to detect CVE-2021-31755
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id cve-2021-31755 -u https://target- Template
- Tenda Router AC11 - Remote Command Injection
- Severity
- critical
- Impact
- Successful exploitation of this vulnerability could lead to unauthorized access, data exfiltration, and complete compromise of the affected router.
- Remediation
- Apply the latest firmware update provided by Tenda to fix the remote command injection vulnerability (CVE-2021-31755).
Template by ProjectDiscovery nuclei-templates (gy741), MIT licensed. View the full template. Scan only systems you are authorised to test.
Frequently Asked Questions
Is CVE-2021-31755 being exploited in your environment?
Detect and block the exploit chain at execution, on systems you cannot patch yet.