Threats / Tenda / CVE-2021-31755
CVE-2021-31755
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
Tenda AC11 Router vulnerability
Tenda AC11 routers contain a stack buffer overflow in the /goform/setmac endpoint that allows remote code execution via crafted POST requests.
Verdict
Today item — known-exploited.
A stack buffer overflow vulnerability in Tenda AC11 routers enables unauthenticated remote code execution. The high EPSS score and active exploitation in the wild indicate immediate risk to deployed devices.
CISA KEV Yes · 2021-11-034EPSS 0.85849 (verify live)5CVSS 9.8 (CISA)3CISA SSVC Exploitation: active · Automatable: yes · Impact: total3Exploit Public PoC / detection · nuclei template11
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
677 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03).
Probability (EPSS)
EPSS 0.85849 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) · Affected: Tenda, AC11 Router. Confirm exact fixed builds in the vendor advisory.CVSS — CISA-assigned via the ADP container (CVE.org), version 3.1; the CNA left no metrics, so CISA's own score is used ahead of NVD.
Weakness (CWE)
Mapped to CWE-787 Out-of-bounds Write — weakness family: Memory safety.CWE assignment from the public NVD record (may be stale); the weakness class drives how the flaw is exploited.
CISA SSVC (triage disposition)
Exploitation: active · Automatable: yes · Technical Impact: totalCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.
Currency of the record
CISA added this to its KEV catalog 180 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.
Public exploit available
Public exploit tooling is catalogued for this CVE (a public proof-of-concept / detection template). Catalog entries: nuclei template. We link the catalog page(s) only — no payload or code is hosted or restated here.Link, never host — the catalog page is the source; basicsecurity.net does not redistribute payloads.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a POST request to /goform/setmac with an oversized payload to overflow the stack buffer.
Business
Attacker gains arbitrary code execution on the router with device privileges.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I establish persistent access by installing malware or backdoors on the compromised router.
Business
Network perimeter is breached; internal systems become accessible to the attacker.
3
Lateral reach — past segmentation narrative 3
Attacker
I pivot from the router to connected devices and intercept network traffic.
Business
Customer data, credentials, and communications are exposed to surveillance and theft.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05