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Vulnerability record · CVE-2018-5721 · published 17 January 2018

CVE-2018-5721: Asuswrt-merlin out-of-bounds write vulnerability

Asuswrt Merlin · Asuswrt Merlin

Stack-based buffer overflow in the ej_update_variables function in router/httpd/web.c on ASUS routers (when using software from https://github.com/RMerl/asuswrt-merlin) allows web authenticated attackers to execute code via a request that updates a setting. In ej_update_variables, the length of the variable action_script is not checked, as long as it includes a "_wan_if" substring.

8.8 CVSS 3.1 High EPSS 1.9% · top 20.7% CWE-787 · Out-of-bounds write
8.8CVSS 3.1 base score, v2 6.5
1.9%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References, 2 tagged exploit
17 Jun 2026Last modified by NVD

Description

Stack-based buffer overflow in the ej_update_variables function in router/httpd/web.c on ASUS routers (when using software from https://github.com/RMerl/asuswrt-merlin) allows web authenticated attackers to execute code via a request that updates a setting. In ej_update_variables, the length of the variable action_script is not checked, as long as it includes a "_wan_if" substring.

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://www.w0lfzhang.com/2018/01/17/ASUS-router-stack-overflow-in-http-server/ ExploitThird Party Advisory
http://www.w0lfzhang.com/2018/01/17/ASUS-router-stack-overflow-in-http-server/ ExploitThird Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2018-5721), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.