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CVE-2026-15421— Speed Optimizer <= 7.8.0 - Authenticated (Contributor+) Stored Cross-Site Scripting via Image Tag Attributes

Quick assessment

Affected
siteground Speed Optimizer – The All-In-One Performance-Boosting Plugin
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

WordPress 插件 Speed Optimizer – The All-In-One Performance-Boosting Plugin 存在存储型跨站脚本（Stored Cross-Site Scripting, XSS）漏洞，影响范围为所有等于或低于 7.8.0 的版本。该漏洞是由于输入清理和输出转义不足所致。攻击者可以通过图像标签属性注入恶意脚本，当其他用户访问被注入的页面时，这些脚本便会执行。要利用此漏洞，攻击者需要具有贡献者级别（contributor）或更高的权限，并且网站管理员必须在插件设置

CVSS 6.4 · Medium EPSS 0.30% · P22

Affected Version Matrix 1

VendorProduct Version RangeStatus
siteground Speed Optimizer – The All-In-One Performance-Boosting Plugin ≤ 7.8.0 affected
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I. Basic Information for CVE-2026-15421

Vulnerability Information
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Vulnerability Title
Speed Optimizer <= 7.8.0 - Authenticated (Contributor+) Stored Cross-Site Scripting via Image Tag Attributes
Source: CVE Program / CVE List V5
Vulnerability Description
The Speed Optimizer – The All-In-One Performance-Boosting Plugin plugin for WordPress is vulnerable to Stored Cross-Site Scripting via Image Tag Attributes in all versions up to, and including, 7.8.0 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This is only exploitable when the site administrator has enabled the Lazy Load Media option in the plugin settings.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
siteground Speed Optimizer – The All-In-One Performance-Boosting Plugin 0 ~ 7.8.0 -

II. Public POCs for CVE-2026-15421

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III. Intelligence Information for CVE-2026-15421

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Patches & Fixes for CVE-2026-15421 (4)

Vendor Advisories for CVE-2026-15421 (1)

Vendor Pages for CVE-2026-15421 (2)

IV. Related Vulnerabilities

Same product: Speed Optimizer – The All-In-One Performance-Boosting Plugin
Same vendor: siteground
Same weakness: CWE-79

V. Comments for CVE-2026-15421

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