Cross-Site Scripting Vulnerability in justhtml by Emil Stenstrom
CVE-2026-5389

5.1MEDIUM

Key Information:

Vendor

Emilstenstrom

Status
Justhtml
Vendor
CVE Published:
23 August 2026

What is CVE-2026-5389?

The justhtml library, up to version 1.12.0, contains a cross-site scripting vulnerability that exists in the to_markdown() function. This flaw allows attackers to manipulate pre tags containing backticks, thus breaching the intended security measures of fixed-length code fences. If the Markdown generated by justhtml is rendered using CommonMark or GFM-style renderers, it can lead to the execution of raw HTML, potentially compromising user data and site integrity.

Affected Version(s)

justhtml 0 < 1.13.0

justhtml 1.13.0

References

https://github.com/EmilStenstrom/justhtml/security/adviso...
vendor-advisory
https://www.vulncheck.com/advisories/justhtml-before-xss-...
third-party-advisory

CVSS V4

Score:
5.1
Severity:
MEDIUM
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
Unknown

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

AlfinJ0se
.