CVE-2026-49449: Joplin: KaTeX `trust:true` enables URL-allowlist bypass leading to NTLMv2 credential theft via UNC path on Windows
Joplin is an open source note-taking and to-do application that organises notes and lists into notebooks. From 1.4.0 until 3.7.2, packages/renderer/MdToHtml/rules/katex.ts enables KaTeX's trust option for note content, allowing a note author to place a \href URL into rendered output without passing Joplin's normal URL allowlist. On Windows, clicking a link whose target is an attacker-controlled UNC path causes pathExists() to initiate SMB authentication and disclose the current user's NTLMv2 challenge-response without a warning. The unfiltered URL can also invoke other registered URL handlers, but the credential disclosure through KaTeX \href is the distinguishing demonstrated impact. This issue is fixed in version 3.7.2.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Joplinto a version that resolves this vulnerability.Fixed in 3.7.2
Event History
Frequently Asked Questions
Which users are exposed to NTLMv2 credential disclosure?
Windows users running affected Joplin versions are exposed if they render attacker-controlled note content and click a KaTeX \href link targeting an attacker-controlled UNC path. The affected version range is 1.4.0 through versions before 3.7.2.
What interaction is required for exploitation?
An attacker must provide note content containing a KaTeX \href URL, and the user must click the rendered link. The demonstrated credential-disclosure impact occurs when that URL is an attacker-controlled UNC path.
Is this caused by Joplin's normal URL allowlist?
No. The KaTeX renderer enabled the trust option for note content, allowing \href URLs to be rendered without passing through Joplin's normal URL allowlist.
How can the issue be remediated?
Upgrade Joplin to version 3.7.2, which fixes the issue. Until upgrading, avoid clicking KaTeX-rendered links in untrusted note content, particularly links that may point to UNC paths or other nonstandard URL handlers.