A stack overflow vulnerability exists in the httpd service in ASUS RT-AX56U Router Version 3.0.0.4.386.44266.

published 2022-10-06 4y ago modified 2026-06-17 4mo ago also EUVD-2021-27731

cvss: 8.8; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.6%; EPSS 1.6% chance of exploitation in 30 days, percentile 76%
public exploits: 0; none known

A stack overflow vulnerability exists in the httpd service in ASUS RT-AX56U Router Version 3.0.0.4.386.44266. This vulnerability is caused by the strcat function called by "caupload" input handle function allowing the user to enter 0xFFFF bytes into the stack. This vulnerability allows an attacker to execute commands remotely. The vulnerability requires authentication.

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Exploit prediction

1.63% chance of exploitation in the next 30 days, higher than 76% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

x1ng.top https://x1ng.top/2021/10/14/ASUS%E6%A0%88%E6%BA%A2%E5%87%BA%E6%BC%8F%E6%B4%9E%E5%88%86%E6%9E%90/ referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
NVD	3.1	8.8	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Classification

Weakness

CWE-787 Out-of-bounds Write

References

x1ng.top /2021/10/14/ASUS%E6%A0%88%E6%BA%A2%E5%87%BA%E6%BC%8F%E6%B4%9E%E5%88%86%E6%9E%90/
exploit, third-party-advisory
asus.com /tw/Networking-IoT-Servers/WiFi-Routers/ASUS-WiFi-Routers/RT-AX56U/HelpDesk_BIOS/
product, vendor-advisory

Sources

CVE List CVE-2021-40556
NVD CVE-2021-40556

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