CVE-2025-66121Network attack vector

Unauthenticated service interruption via missing capability check

Published Dec 16, 2025 · Updated Dec 16, 2025

Missing authorization in SiteGround Security Optimizer 1.5.8 and earlier allows remote attackers to interrupt service. The affected function performs an unauthorized action without a capability check, but the function and action are not publicly identified. No account or user interaction is required; published scoring limits the demonstrated consequence to reduced availability.

CVSS severity5.3
Medium
EPSS probability0.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Missing authorization in SiteGround Security Optimizer 1.5.8 and earlier allows remote attackers to interrupt service. The affected function performs an unauthorized action without a capability check, but the function and action are not publicly identified. No account or user interaction is required; published scoring limits the demonstrated consequence to reduced availability.

The record

CVE
CVE-2025-66121
Published
Dec 16, 2025
Updated
Dec 16, 2025
Vendor
SiteGround
Product
Security Optimizer
Classifications
CWE-862
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 16, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 16, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=n/a <=<= 1.5.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

SiteGround · Security Optimizerversion=n/a <=<= 1.5.8

Published CVSS scores

5.3PatchstackCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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

CWE-862Missing Authorization

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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