Stored XSS via predictable minifier placeholders
Published May 18, 2026 · Updated May 18, 2026
Stored XSS in Autoptimize before 3.1.15, Clearfy Cache before 2.4.2, and Speed Optimizer before 7.7.9 lets remote attackers inject script. Their HTML minifier creates placeholders from the MD5 hash of request time and a counter, then a regular expression replaces attacker-supplied lookalikes with protected markup. Exploitation requires synchronized server time, an approved malicious comment, a visitor who loads that post, and HTML minification enabled for Speed Optimizer and Clearfy Cache.
Summary
What happened
Stored XSS in Autoptimize before 3.1.15, Clearfy Cache before 2.4.2, and Speed Optimizer before 7.7.9 lets remote attackers inject script. Their HTML minifier creates placeholders from the MD5 hash of request time and a counter, then a regular expression replaces attacker-supplied lookalikes with protected markup. Exploitation requires synchronized server time, an approved malicious comment, a visitor who loads that post, and HTML minification enabled for Speed Optimizer and Clearfy Cache.
The record
- CVE
- CVE-2026-3220
- Published
- May 18, 2026
- Updated
- May 18, 2026
- Vendor
- SiteGround
- Product
- Speed Optimizer
- Classifications
- CWE-79, T1059.007
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 18, 2026CVE publishedPublication date reported by the CVE source.
- May 18, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <7.7.9
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Weakness, pattern, technique
Public exploit references
- WPScan synchronized-placeholder Python proof of conceptfunctional · validated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo