CVE-2021-35395: in the CISA KEV catalogue
Realtek AP-Router SDK Buffer Overflow Vulnerability. CISA added CVE-2021-35395 to the Known Exploited Vulnerabilities catalogue on 2021-11-03 with a default due date of 2021-11-17. Known ransomware campaign use: Unknown. Forensic triage flag: No.
Realtek AP-Router SDK HTTP web server boa contains a buffer overflow vulnerability due to unsafe copies of some overly long parameters submitted in the form that lead to denial-of-service (DoS). (CISA description)
- Vendor / product
- Realtek AP-Router SDK
- CWE
- CWE-20, CWE-122
- CISA required action
- Apply updates per vendor instructions.
- EPSS
- 98%, percentile 99 (scored 2026-11-03)
EPSS puts about 98 in 100 odds (98%) on exploitation activity being observed in the next 30 days. Its score is higher than or equal to that of 99% of scored CVEs. This is a model estimate about exploitation anywhere, not about your environment.
Vendor and reference links (from CISA)
Your own deadline under CISA BOD 26-04 depends on exposure, automatability and technical impact: work it out with the BOD 26-04 calculator.
Frequently asked questions
Is CVE-2021-35395 in the CISA KEV catalogue?
Yes. CISA added CVE-2021-35395 (Realtek AP-Router SDK Buffer Overflow Vulnerability) to the Known Exploited Vulnerabilities catalogue on 2021-11-03. CISA's default due date for it is 2021-11-17.
Is CVE-2021-35395 used in ransomware attacks?
CISA marks known ransomware campaign use as Unknown for CVE-2021-35395. That means CISA lacks confirmation, not that ransomware groups do not use it.
What should I do about CVE-2021-35395?
CISA's required action: Apply updates per vendor instructions.
Sources
- CISA, Known Exploited Vulnerabilities Catalog (accessed 2026-11-03)
- FIRST, Exploit Prediction Scoring System (EPSS) (EPSS by FIRST; scores generated by Empirical Security)
- NVD record for CVE-2021-35395