How severe is CVE-2021-40556?

CVE-2021-40556 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-40556 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (68th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-40556?

CVE-2021-40556 affects Asus Rt-ax56u Firmware. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-40556?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-40556 published?

CVE-2021-40556 was published on 2022-10-06 and last updated on 2026-06-17.

CVE-2021-40556

CVE-2021-40556 is a high-severity vulnerability in Asus Rt-ax56u Firmware with a CVSS 3.x base score of 8.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-787.

Key facts

Severity: High (CVSS 3.x base score 8.8)
EPSS exploit prediction: 1% (68th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-787
Affected product: Asus Rt-ax56u Firmware
Published: 2022-10-06
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2021-40556?: 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.
How severe is CVE-2021-40556?: CVE-2021-40556 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-40556 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (68th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-40556?: CVE-2021-40556 affects Asus Rt-ax56u Firmware. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-40556?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-40556 published?: CVE-2021-40556 was published on 2022-10-06 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:o:asus:rt-ax56u_firmware:3.0.0.4.386.44266:*:*:*:*:*:*:*

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