CVE-2018-5721
CVE-2018-5721 is a high-severity vulnerability in Asuswrt-merlin 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)
- CVSS v2: 6.5
- EPSS exploit prediction: 2% (78th percentile)
- Actively exploited: Not listed in CISA KEV
- Weakness: CWE-787
- Affected product: Asuswrt-merlin
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2018-5721?
- 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.
- How severe is CVE-2018-5721?
- CVE-2018-5721 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-2018-5721 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (78th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2018-5721?
- CVE-2018-5721 affects Asuswrt-merlin. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2018-5721?
- 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-2018-5721 published?
- CVE-2018-5721 was published on 2018-01-17 and last updated on 2026-06-17.
References
Affected products (1)
- cpe:2.3:o:asuswrt-merlin:asuswrt-merlin:*:*:*:*:*:*:*:*
More vulnerabilities in Asuswrt-merlin
- CVE-2017-12754 — High (CVSS 8.8): Stack buffer overflow in httpd in Asuswrt-Merlin firmware 380.67_0RT-AC5300 and earlier for ASUS devices and ASUS…
- CVE-2018-8878 — Medium (CVSS 5.3): Information disclosure in Asuswrt-Merlin firmware for ASUS devices older than 384.4 and ASUS firmware before…
- CVE-2018-8877 — Medium (CVSS 5.3): Information disclosure in Asuswrt-Merlin firmware for ASUS devices older than 384.4 and ASUS firmware before…
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