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TI-2021-17582 Aliases CVE-2021-40556GHSA-9v8q-97m7-4x6q

A stack overflow vulnerability exists in the httpd service in ASUS RT-AX56U Router…

Priority MEDIUM 41CWE-787Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Impact type
Code execution
Confidentiality · integrity · availability
High · High · High
Fix status
No fix listed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA. Impact type from CWE-787 and the CVSS impact.

Summary

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.

Why it matters now

EPSS 0.01633 76th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix No fix listed No fixed version in the sources yet

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

VendorProductAffected versionsFixed inStatusSource
——all versions—No fix listedCNA
  • — Vendor— Affected all versions Fixed in — No fix listed CNA

CPE configurations NVD · 2

CPEVersionsRoleVendor
cpe:2.3:o:asus:rt-ax56u_firmware:3.0.0.4.386.44266:*:*:*:*:*:*:*3.0.0.4.386.44266VulnerableASUS
cpe:2.3:h:asus:rt-ax56u:-:*:*:*:*:*:*:*not specified by NVDRunning onASUS
  • cpe:2.3:o:asus:rt-ax56u_firmware:3.0.0.4.386.44266:*:*:*:*:*:*:* Versions 3.0.0.4.386.44266 Vulnerable ·ASUS
  • cpe:2.3:h:asus:rt-ax56u:-:*:*:*:*:*:*:* Versions not specified by NVD Running on ·ASUS

Remediation

No fixed version listed by the sources yet.

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-40556
  2. 2026-10-03 Alias added: GHSA-9v8q-97m7-4x6q

References

Exploit 1

Advisory 1

  • TI-2022-09749 Out-of-bounds write in Asuswrt-Merlin New Gen CVSS 3.1CRITICAL 9.8
  • TI-2021-18228 A brute-force protection bypass in CAPTCHA protection in ASUS ROG Rapture GT-AX11000… CVSS 3.1CRITICAL 9.8
  • TI-2021-02220 In ASUS RT-AX3000, ZenWiFi AX (XT8), RT-AX88U, and other ASUS routers with firmware <… CVSS 3.1HIGH 7.5
  • TI-2021-19533 ASUS RT-A88U 3.0.0.4.386_45898 is vulnerable to Cross Site Scripting (XSS). CVSS 3.1CRITICAL 9.0
  • TI-2021-18229 An HTTP request smuggling in web application in ASUS ROG Rapture GT-AX11000, RT-AX3000… CVSS 3.1HIGH 7.5
  • TI-2022-07938 ASUS RT-AX56U - Stack overflew CVSS 3.1HIGH 8.8
See all 11 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences