CVE-2021-25811Network attack vector

Persistent web-service outage via crafted HTTP parameter

Published Apr 29, 2021 · Updated Aug 3, 2024

Denial of service in MERCUSYS Mercury X18G 1.0.5 allows remote attackers to disable the web server through a crafted HTTP POST value. The device accepts and persists the crafted listen_http_lan value in uhttpd.json, leaving the HTTP service unable to start after a reboot. No authentication or user interaction is required, and the service interruption persists across subsequent device restarts.

CVSS severity7.5
High
EPSS probability1.63%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in MERCUSYS Mercury X18G 1.0.5 allows remote attackers to disable the web server through a crafted HTTP POST value. The device accepts and persists the crafted listen_http_lan value in uhttpd.json, leaving the HTTP service unable to start after a reboot. No authentication or user interaction is required, and the service interruption persists across subsequent device restarts.

The record

CVE
CVE-2021-25811
Published
Apr 29, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 29, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.8NIST National Vulnerability DatabaseAV:N/AC:L/Au:N/C:N/I:N/A:C
7.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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