How severe is CVE-2021-25811?

CVE-2021-25811 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-25811 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (73rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-25811?

CVE-2021-25811 affects Mercusys Mercury X18g Firmware. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-25811?

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-2021-25811 published?

CVE-2021-25811 was published on 2021-04-29 and last updated on 2026-06-17.

CVE-2021-25811

CVE-2021-25811 is a high-severity vulnerability in Mercusys Mercury X18g Firmware with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 7.8
EPSS exploit prediction: 2% (73rd percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Mercusys Mercury X18g Firmware
Published: 2021-04-29
Last modified: 2026-06-17

Description

MERCUSYS Mercury X18G 1.0.5 devices allow Denial of service via a crafted value to the POST listen_http_lan parameter. Upon subsequent device restarts after this vulnerability is exploted the device will not be able to access the webserver unless the listen_http_lan parameter to uhttpd.json is manually fixed.

Frequently asked questions

What is CVE-2021-25811?: MERCUSYS Mercury X18G 1.0.5 devices allow Denial of service via a crafted value to the POST listen_http_lan parameter. Upon subsequent device restarts after this vulnerability is exploted the device will not be able to access the webserver unless the listen_http_lan parameter to uhttpd.json is manually fixed.
How severe is CVE-2021-25811?: CVE-2021-25811 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-25811 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (73rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-25811?: CVE-2021-25811 affects Mercusys Mercury X18g Firmware. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-25811?: 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-2021-25811 published?: CVE-2021-25811 was published on 2021-04-29 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:o:mercusys:mercury_x18g_firmware:1.0.5:*:*:*:*:*:*:*

More vulnerabilities in Mercusys Mercury X18g Firmware

CVE-2021-25810 — Medium (CVSS 6.1): Cross site Scripting (XSS) vulnerability in MERCUSYS Mercury X18G 1.0.5 devices, via crafted values to the…
CVE-2021-23242 — Medium (CVSS 5.3): MERCUSYS Mercury X18G 1.0.5 devices allow Directory Traversal via ../ to the UPnP server, as demonstrated by the…
CVE-2021-23241 — Medium (CVSS 5.3): MERCUSYS Mercury X18G 1.0.5 devices allow Directory Traversal via ../ in conjunction with a loginLess or login.htm URI…

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