CVE-2026-41159
Description
A flaw was found in Mermaid, a JavaScript tool for creating diagrams and charts. A remote attacker could exploit this vulnerability by injecting malicious Cascading Style Sheets (CSS) through specific configuration options, such as fontFamily, themeCSS, and altFontFamily. This injected CSS can bypass the intended scoping, allowing styles to be applied to all elements on a web page, leading to page defacement. Additionally, this flaw enables the exfiltration of sensitive information from the Document Object Model (DOM) using CSS selectors.
Statement
This Moderate flaw in Mermaid, a JavaScript diagramming tool, allows for CSS injection that bypasses intended scoping. A remote attacker could exploit this by providing a specially crafted diagram, leading to page defacement and potential exfiltration of sensitive information from the Document Object Model (DOM). This impact is considered Moderate as it requires user interaction to render the malicious content.
Mitigation
Upgrade to Mermaid 11.8.1 or later. As a workaround, sanitize or reject user-supplied diagram definitions before rendering, or render diagrams in a sandboxed iframe with restricted CSP to limit the impact of CSS injection.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.4 | 5.3 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | Low | None | N/A |
| User Interaction | Required | None | N/A |
| Scope | Changed | Unchanged | N/A |
| Confidentiality | Low | None | N/A |
| Integrity Impact | Low | None | N/A |
| Availability Impact | None | Low | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Understanding the Weakness (CWE)
Access Control,Confidentiality
Technical Impact: Bypass Protection Mechanism; Read Application Data
The most common attack performed with cross-site scripting involves the disclosure of private information stored in user cookies, such as session information. Typically, a malicious user will craft a client-side script, which -- when parsed by a web browser -- performs some activity on behalf of the victim to an attacker-controlled system (such as sending all site cookies to a given E-mail address). This could be especially dangerous to the site if the victim has administrator privileges to manage that site. This script will be loaded and run by each user visiting the web site. Since the site requesting to run the script has access to the cookies in question, the malicious script does also.
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
In some circumstances it may be possible to run arbitrary code on a victim's computer when cross-site scripting is combined with other flaws, for example, "drive-by hacking."
Confidentiality,Integrity,Availability,Access Control
Technical Impact: Execute Unauthorized Code or Commands; Bypass Protection Mechanism; Read Application Data
The consequence of an XSS attack is the same regardless of whether it is stored or reflected. The difference is in how the payload arrives at the server. XSS can cause a variety of problems for the end user that range in severity from an annoyance to complete account compromise. Some cross-site scripting vulnerabilities can be exploited to manipulate or steal cookies, create requests that can be mistaken for those of a valid user, compromise confidential information, or execute malicious code on the end user systems for a variety of nefarious purposes. Other damaging attacks include the disclosure of end user files, installation of Trojan horse programs, redirecting the user to some other page or site, running "Active X" controls (under Microsoft Internet Explorer) from sites that a user perceives as trustworthy, and modifying presentation of content.
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