Reliance on Untrusted Inputs in a Security Decision in KaTeX - CVE-2026-103923
Published: November 9, 2026
Vulnerability identifier: #VU162926
CSH Severity: Medium
CVSS v4: 2.1 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-103923
CWE-ID: CWE-807
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows an unauthenticated attacker to bypass KaTeX trust restrictions and cause cross-site scripting when a victim follows a generated link.
The vulnerability exists due to KaTeX accepting an inherited trust setting when prototype pollution already exists or the renderer options prototype is attacker-controlled. An unauthenticated attacker can supply mathematical expressions that generate malicious links if the application inserts the rendered output into a web page without separate sanitization.
Affected software
KaTeX
Fedora
nextcloud
Fedora
nextcloud
How to mitigate CVE-2026-103923
Install security update from vendor's website.
KaTeX - update to 0.18.2
nextcloud - addressed in versions 35.0.2-1.el10_2, 35.0.2-1.el10_3, 35.0.2-1.el10_4, 35.0.2-1.fc43, 35.0.2-1.fc44, 35.0.2-1.fc45
nextcloud - addressed in versions 35.0.2-1.el10_2, 35.0.2-1.el10_3, 35.0.2-1.el10_4, 35.0.2-1.fc43, 35.0.2-1.fc44, 35.0.2-1.fc45