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Fencer Vulns
high 8.2

CVE-2024-26151 json

Potentially untrusted input is rendered as HTML in final output

published 2024-02-22 2 y ago modified 2026-09-10 1 mo ago also GHSA-578p-fxmm-6229 , PYSEC-2026-1631 , EUVD-2024-0518

cvss
8.2
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 50%
public exploits
0
none known

Summary

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 `&lt;script&gt;` 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.

Patch / fix

  • pypi mjml 0.11.0
  • FelixSchwarz mjml-python 0.11.0

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
2 y ago

Exploit prediction

0.62% chance of exploitation in the next 30 days, higher than 50% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/FelixSchwarz/mjml-python/issues/52 referenced PoC, tagged "exploit" by a source, unverified
  • vicarius.io https://www.vicarius.io/vsociety/posts/cve-2024-26151-mjml-python-vulnerability-1 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:H/A:L
NVD 3.1 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
OSV 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:H/A:L
GitHub 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:H/A:L

Affected packages

ecosystem package affected fixed in
pypi mjml
>=0.10.0, <0.11.0
0.11.0

Affected products

  • FelixSchwarz mjml-python

Classification

Weakness
  • CWE-20 Improper Input Validation
  • CWE-79 Improper Neutralization of Input During Web Page Generation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.