Cyber Resilience

CVE-2025-8939

Memory Safety in Tenda Ac20 Firmware 16.03.08.0 – 16.03.08.12

Public PoCMemory Safety
Published
14 August 2025
Modified
17 June 2026
Patch / advisory
View advisory
CVSS Score v4 7.4
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0088 56th percentile
Risk Priority 40 floored blend · peak EPSS

Summary

CVE-2025-8939 is a high-severity Improper Restriction of Operations within the Bounds of a Memory Buffer (CWE-119) vulnerability in Tenda Ac20 Firmware. Its CVSS base score is 7.4 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked in the top 44% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.

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 vulnerability identified as CVE-2025-8939 affects Tenda AC20 routers running firmware up to version 16.03.08.12. It resides in an unspecified function within the /goform/WifiGuestSet endpoint, where improper handling of the shareSpeed argument triggers a buffer overflow. The issue is tracked under CWE-119 and CWE-120 and carries a CVSS 4.0 score of 7.4, reflecting network-accessible attack conditions with low complexity and high impact on confidentiality, integrity, and availability.

An authenticated remote attacker can supply a crafted shareSpeed value to the affected endpoint, causing memory corruption that may lead to arbitrary code execution or denial of service. Public proof-of-concept code has been released, confirming that exploitation is feasible over the network without user interaction once valid credentials are obtained.

The EPSS score remains flat at 0.0155 with no material increase since disclosure. Available references consist of public disclosure and proof-of-concept repositories rather than vendor advisories describing patches or configuration mitigations.

EU & UK References

Vulnerability Data

A vulnerability was determined in Tenda AC20 up to 16.03.08.12. Affected is an unknown function of the file /goform/WifiGuestSet. The manipulation of the argument shareSpeed leads to buffer overflow. It is possible to launch the attack remotely. The exploit has…

more

been disclosed to the public and may be used.

CWE(s)
CWE-119CWE-120

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 →
T1055 Process Injection Stealth
Adversaries may inject code into processes in order to evade process-based defenses as well as possibly elevate privileges.
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-2025-11385Same product: Tenda Ac20
CVE-2025-15356Same product: Tenda Ac20
CVE-2025-8940Same product: Tenda Ac20
CVE-2025-10815Same product: Tenda Ac20
CVE-2025-13258Same product: Tenda Ac20
CVE-2025-14656Same product: Tenda Ac20
CVE-2025-10120Same product: Tenda Ac20
CVE-2025-8160Same product: Tenda Ac20
CVE-2025-9089Same product: Tenda Ac20
CVE-2025-9046Same product: Tenda Ac20

Affected Assets

tenda
ac20 firmware
16.03.08.0 — 16.03.08.12

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V17.3.2
  • V5.2.1

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and analysis can find missing size checks before deployment.

SI-10 Information Input Validation good match

Input validation directly enforces size checks before buffer copies.

SA-8 Security and Privacy Engineering Principles partial match

Secure engineering principles require memory-safe design and coding that structurally avoids buffer-boundary violations.

SI-16 Memory Protection partial match

Memory protection restricts exploitation impact of buffer overflows without eliminating the underlying coding flaw.

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 SDLC practices (bounds checking, safe APIs, reviews) directly prevent this class of flaw.

ID.RA-01 partial match
prevents

Vulnerability scanning and code analysis directly surface buffer-boundary flaws.

ID.RA-08 partial match
prevents

Receiving and triaging vulnerability disclosures commonly includes buffer-related reports.

PR.AT-02 partial match
prevents

Developer training on secure coding reduces introduction of memory-buffer errors.

PR.PS-02 partial match
prevents

Patching replaces vulnerable code containing buffer-boundary defects.

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.8.28 Secure coding mostly match
prevents

Secure coding directly requires bounds-checked memory operations, addressing the root cause of CWE-120.

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

Security testing in development catches out-of-bounds accesses before release, covering most instances of the weakness.

A.8.25 Secure development life cycle partial match
prevents

Secure development lifecycle mandates memory-safety practices that directly prevent buffer-boundary violations.

A.8.26 Application security requirements partial match
prevents

Application security requirements can specify memory-safety rules, but do not prescribe implementation details.

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

Secure architecture and engineering principles include memory-safe design patterns that mitigate buffer overflows.

References