What is CVE-2020-36109?

CVE-2020-36109 is a critical-severity vulnerability in ASUS Rt-Ax86u, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.8/10. Published 2021-02-01.

How severe is CVE-2020-36109?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2020-36109 known to be exploited?

6 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Buffer overflow in ASUS Rt-Ax86u

CVE-2020-36109

ASUS RT-AX86U router firmware below version under 9.0.0.4_386 has a buffer overflow in the blocking_request.cgi function of the httpd module that can cause code execution when an attacker constructs malicious data.

Vulnerability class: Buffer Overflow

Published 2021-02-01 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.042 (90.6th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 91st percentile — 90.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.042 · newest: 0.042 · change: 0.000

Affected products

Weakness classification (CWE)

CWE-120 — Buffer Copy without Checking Size of Input (Classic Buffer Overflow)

Public proof-of-concept exploits

References

www.asus.com/Static_WebPage/ASUS-Product-Security-Advisory/ (Vendor Advisory)

Frequently asked questions

What is CVE-2020-36109?: CVE-2020-36109 is a critical-severity vulnerability in ASUS Rt-Ax86u, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.8/10. Published 2021-02-01.
How severe is CVE-2020-36109?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2020-36109 known to be exploited?: 6 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.