Reflected XSS via post-validation ESI parameter replacement
Published Sep 19, 2026 · Updated Sep 19, 2026
Reflected XSS in LiteSpeed Cache for WordPress 7.9 and earlier allows remote attackers to inject script through the ESI request path. ESI handling validates a signed esi query value but later reads PHP's merged request data, letting a POST esi field replace the validated block data without adequate output escaping. Exploitation requires a valid signed query value and user interaction with a crafted request; executed script can read or alter data available to the victim's browser session.
Summary
What happened
Reflected XSS in LiteSpeed Cache for WordPress 7.9 and earlier allows remote attackers to inject script through the ESI request path. ESI handling validates a signed esi query value but later reads PHP's merged request data, letting a POST esi field replace the validated block data without adequate output escaping. Exploitation requires a valid signed query value and user interaction with a crafted request; executed script can read or alter data available to the victim's browser session.
The record
- CVE
- CVE-2026-76579
- Published
- Sep 19, 2026
- Updated
- Sep 19, 2026
- Vendor
- LiteSpeed Technologies
- Product
- LiteSpeed Cache for WordPress
- Classifications
- CWE-79, T1204.001
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 19, 2026CVE publishedPublication date reported by the CVE source.
- Sep 19, 2026Record 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.
- Affected versionversion=0 <=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.
Activity data is delayed. The latest report is Sep 28, 2026.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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