CVE-2026-75834Network attack vector

Stored XSS via invalid UTF-8 bypass

Published Aug 18, 2026 · Updated Aug 18, 2026

Stored XSS in Security::detectXss() in Grav before 2.0.14 allows remote authenticated users to run script in visitors' browsers. All regex checks in system/src/Grav/Common/Security.php use PCRE UTF-8 mode, so one invalid byte makes preg_match() fail for every rule and Validation::checkSafety() accepts malicious page content as clean. Exploitation requires page-edit permissions outside the security.xss_whitelist; stored JavaScript then executes for any viewer of the affected page, including administrators who browse it.

CVSS severity5.1
Medium
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in Security::detectXss() in Grav before 2.0.14 allows remote authenticated users to run script in visitors' browsers. All regex checks in system/src/Grav/Common/Security.php use PCRE UTF-8 mode, so one invalid byte makes preg_match() fail for every rule and Validation::checkSafety() accepts malicious page content as clean. Exploitation requires page-edit permissions outside the security.xss_whitelist; stored JavaScript then executes for any viewer of the affected page, including administrators who browse it.

The record

CVE
CVE-2026-75834
Published
Aug 18, 2026
Updated
Aug 18, 2026
Vendor
Grav
Product
Grav
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 18, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 18, 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.

  1. Affected versionversion=0 <2.0.14

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Grav · Gravversion=0 <2.0.14

Published CVSS scores

5.1GitHub Advisory DatabaseCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007JavaScript

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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