Threats / Realtek / CVE-2021-35395
CVE-2021-35395
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
Realtek AP-Router SDK vulnerability
Realtek AP-Router SDK contains a buffer overflow in the boa HTTP web server caused by unsafe handling of overly long form parameters, enabling denial-of-service attacks.
Verdict
Today item — known-exploited.
A remotely exploitable buffer overflow in the boa web server component of Realtek AP-Router SDK allows unauthenticated attackers to crash the service. The high EPSS score and active exploitation in the wild indicate significant risk to deployed router infrastructure.
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
663 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 0.98059 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: Realtek, AP-Router SDK. Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-20 Improper Input Validation, CWE-122 Heap-based Buffer Overflow — weakness family: Memory safety.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
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 HTTP requests with oversized form parameters targeting the boa web server.
Business
Router availability is disrupted, interrupting network connectivity for end users.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I trigger the buffer overflow to cause the web server process to crash repeatedly.
Business
Management and configuration interfaces become inaccessible, preventing legitimate administration.
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