Grav before 2.0.14 Stored XSS via Invalid UTF-8 Byte

published 2026-08-18 2 mo ago modified 2026-10-22 17 d ago also GHSA-q2j8-x8hf-63ch , EUVD-2026-60598

cvss: 5.4; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 17%
public exploits: 0; none known

Grav before 2.0.14 contains a stored cross-site scripting vulnerability in the Security::detectXss() function (system/src/Grav/Common/Security.php). All XSS detection patterns use the PCRE /u (UTF-8) modifier, so a single invalid UTF-8 byte anywhere in page content causes preg_match() to return false for every pattern, silently bypassing the save-time XSS safety gate (Validation::checkSafety()). An authenticated attacker with page-edit permissions (without the security.xss_whitelist privilege) can store malicious JavaScript that executes in the browser of a visitor who views the affected page.

Patch / fix

fixed in 2

packagist getgrav/grav 2.0.14
getgrav grav 2.0.14

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 2 mo ago (2026-08-18)

Exploit prediction

0.26% chance of exploitation in the next 30 days, higher than 17% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	4.0	5.1	CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
CNA	3.1	5.4	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
CNA	4.0	5.1	CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
GitHub	3.1	5.4	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
packagist	getgrav/grav	<2.0.14	2.0.14

Affected products

getgrav grav

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

github.com /getgrav/grav/security/advisories/GHSA-q2j8-x8hf-63ch
vendor-advisory, web
vulncheck.com /advisories/grav-before-stored-xss-via-invalid-utf-8-byte
third-party-advisory, web
nvd.nist.gov /vuln/detail/CVE-2026-75834
advisory
github.com /getgrav/grav
package

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary