Potentially untrusted input is rendered as HTML in final output

MITTEL 5.4CVE-2024-26151 · GHSA-578p-fxmm-6229 · PYSEC-2026-1631 · Published 22/02/2024 · updated 17/06/2026

Kurz gesagt

CVE-2024-26151 ist eine Schwachstelle (MITTEL (CVSS 5.4)) in mjml, mjml-python (felixschwarz).
Wahrscheinlichkeit einer Ausnutzung in den nächsten 30 Tagen (EPSS): 0.62%, höher als bei 50.0% aller Schwachstellen.
Abhilfe: auf 0.11.0 oder neuer aktualisieren.

Package	Affected versions	Patched versions
mjml PyPI	`≥ 0.10.0, < 0.11.0`	`0.11.0`
mjml-python felixschwarz	`= 0.10.0`	No fix yet

Description

Impact

All users of mjml-python who insert untrusted data into mjml templates unless that data is checked in a very strict manner. User input like <script> would be rendered as <script> in the final HTML output.

The attacker must be able to control some data which is later injected in an mjml template which is then send out as email to other users. The attacker could control contents of email messages sent through the platform.

Patches

The problem has been fixed in version 0.11.0 of this library. Versions before 0.10.0 are not affected by this security issue which was added as part of commit 84c495da20a91640a1ca551ace17df7f3be644aa.

Workarounds

Ensure that potentially untrusted user input does not contain any sequences which could be rendered as HTML.

References

Initial issue report by @sh-at-cs in #52

NVD description

The `mjml` PyPI package, found at the `FelixSchwarz/mjml-python` GitHub repo, is an unofficial Python port of MJML, a markup language created by Mailjet. All users of `FelixSchwarz/mjml-python` who insert untrusted data into mjml templates unless that data is checked in a very strict manner. User input like `<script>` would be rendered as `<script>` in the final HTML output. The attacker must be able to control some data which is later injected in an mjml template which is then send out as email to other users. The attacker could control contents of email messages sent through the platform. The problem has been fixed in version 0.11.0 of this library. Versions before 0.10.0 are not affected by this security issue. As a workaround, ensure that potentially untrusted user input does not contain any sequences which could be rendered as HTML.