Cyber Resilience

CVE-2021-31755

Memory Safety in Tenda Ac11 Firmware ≤ 02.03.01.104_cn

CISA KEVActive ExploitationEUVD ExploitedPublic PoCMemory Safety
Published
07 May 2021
Modified
10 November 2025
KEV Added
03 November 2021
CVSS Score v3.1 9.8
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.86 99.7th percentile
Risk Priority 97 floored blend · peak EPSS

Summary

CVE-2021-31755 is a critical-severity Out-of-bounds Write (CWE-787) vulnerability in Tenda Ac11 Firmware. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked in the top 0.3% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog; a public proof-of-concept is referenced.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

A stack buffer overflow vulnerability exists in Tenda AC11 wireless routers running firmware versions through 02.03.01.104_CN. The flaw is located in the /goform/setmac endpoint and is tracked as CWE-787. It carries a CVSS 3.1 base score of 9.8, reflecting network-accessible, unauthenticated attack complexity.

An unauthenticated attacker can send a crafted HTTP POST request to the affected endpoint and trigger the overflow to execute arbitrary code on the device. Successful exploitation grants full control of the router, enabling actions such as traffic interception, persistence, or lateral movement within the attached network.

The vulnerability appears in CISA's Known Exploited Vulnerabilities catalog, confirming observed in-the-wild exploitation. Public proof-of-concept material is available in repositories that demonstrate request construction against the setmac handler, underscoring the need for immediate firmware updates or network segmentation where patches are unavailable.

EU & UK References

Vulnerability Data

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.

CWE(s)
CWE-787
KEV Date Added
03 November 2021

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
T1211 Exploitation for Stealth Stealth
Adversaries may exploit vulnerabilities to evade detection by hiding activity, suppressing logging, or operating within trusted or unmonitored components.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2024-57581Same vendor: Tenda
CVE-2023-27013Same vendor: Tenda
CVE-2023-24167Same vendor: Tenda
CVE-2023-50987Same vendor: Tenda
CVE-2023-49042Same vendor: Tenda
CVE-2023-49425Same vendor: Tenda
CVE-2023-25217Same vendor: Tenda
CVE-2023-37718Same vendor: Tenda
CVE-2023-37702Same vendor: Tenda
CVE-2023-51101Same vendor: Tenda

Affected Assets

tenda
ac11 firmware
≤ 02.03.01.104_cn

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

SI-16 Memory Protection
addresses: CWE-787

Out-of-bounds writes that corrupt control flow or inject shellcode are rendered non-executable by the same memory protections.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure-development practices (static analysis, bounds checking, code review) are the primary means of preventing out-of-bounds writes.

ID.RA-01 partial match
prevents

Vulnerability scanning and recording can discover out-of-bounds write flaws so they can be remediated.

PR.PS-02 partial match
prevents

Patching or replacing vulnerable software directly eliminates known instances of this coding weakness.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development and acceptance can detect and prevent out-of-bounds write defects.

A.8.25 Secure development life cycle partial match
prevents

Secure development life cycle mandates practices that prevent out-of-bounds writes.

A.8.26 Application security requirements partial match
prevents

Application security requirements can specify bounds-checking and safe memory handling.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture and engineering principles reduce the likelihood of buffer overflows.

A.8.28 Secure coding partial match
prevents

Secure coding directly addresses out-of-bounds writes through language choice and coding standards.

A.8.32 Change management partial match
prevents

Change management can enforce review gates that catch unsafe memory operations before deployment.

References