Marp Core allows XSS by improper neutralization of HTML sanitization

Marp Core (@marp-team/marp-core) from v3.0.2 to v3.9.0 and v4.0.0, are vulnerable to cross-site scripting (XSS) due to improper neutralization of HTML sanitization.

Impact

Marp Core includes an HTML sanitizer with allowlist support. In the affected versions, the built-in allowlist is enabled by default. When the allowlist is active, if insufficient HTML comments are included, the sanitizer may fail to properly sanitize HTML content and lead cross-site scripting (XSS).

Patches

Marp Core v3.9.1 and v4.0.1 have been patched to fix that.

Workarounds

If you are unable to update the package immediately, disable all HTML tags by setting html: false option in the Marp class constructor.

const marp = new Marp({ html: false })

References

• CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
• https://github.com/marp-team/marp-core/pull/282
• https://github.com/marp-team/marp-core/commit/61a1def244d1b6faa8e2c0be97ec0b68cab3ab49

Credits

Thanks to @Ry0taK for finding out this vulnerability.