# CVE-2026-49449: Joplin: KaTeX `trust:true` enables URL-allowlist bypass leading to NTLMv2 credential theft via UNC path on Windows

> Attackers can steal Windows NTLMv2 credentials by tricking users into clicking malicious links in Joplin notes due to KaTeX trust configuration bypassing URL allowlists.

- **Severity:** Low 2.5 (`CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 21 Sep 2026
- **Updated:** 28 Sep 2026
- **Also known as:** GHSA-9m2r-pv96-jxr3

## What is CVE-2026-49449?

CVE-2026-49449 is a low-severity vulnerability in laurent22 joplin, published on 21 Sep 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

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.

Weakness: CWE-829 (Inclusion of Functionality from Untrusted Control Sphere), CWE-522 (Insufficiently Protected Credentials), CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2026-49449?


## How do I fix CVE-2026-49449?

No fix has been published for CVE-2026-49449 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-49449 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49449 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-49449 and fix it if it is affected.

What it is: CVE-2026-49449 is a low-severity vulnerability in laurent22 joplin, published on 21 Sep 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49449 exists.

Affected product: laurent22 joplin. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-49449/ (Markdown: https://insights.sbomify.com/CVE-2026-49449/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-49449
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-49449
- OSV: https://osv.dev/vulnerability/CVE-2026-49449

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-49449/
Summaries are generated and may contain mistakes; the official description above is the record.