by Kastro
Paper/Archive/CVE-2026-8445

CVE-2026-8445

EmilStenstrom justhtml — justhtml before 1.12.0 Sanitizer Bypass via Markdown

EPSS 0.6%public exploitCVSS 9.8
critical.is priorityof 100
50
CVSS 9.8 (CNA)9.8 / 10 × 3029.4Not in CISA KEV+300.0EPSS percentile 50.4.504 × 2010.1Exploit: SSVC poc+1010.0SSVC exploitation: poc+100.0
Description · from the CVE record

justhtml versions <= 1.11.0 (fixed in 1.12.0) do not sufficiently escape HTML-significant characters (angle brackets) in text nodes when converting a parsed document to Markdown via to_markdown(). While a small set of Markdown metacharacters are escaped, characters such as < and > are preserved, so untrusted input that is safe in to_html() — including entity-decoded text (e.g. &lt;script&gt;) or text from RCDATA/RAWTEXT-parsed elements like <title>, <textarea>, <noscript>, and <plaintext> — can be emitted as raw HTML in the Markdown output, enabling a sanitizer bypass and potential cross-site scripting when that output is rendered.

Affected

ProductAffectedFixed inSource
justhtml< 1.12.01.12.0CNA

Scores by source

VulnCheck (CNA)9.8CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
VulnCheck (CNA)9.3CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CISA ADPSSVCExploitation: poc · Automatable: yes · Technical impact: total

References

exploitgithub.com/EmilStenstrom/justhtml/security/advisories/GHSA-3rcm-vjrc-p45jwriteupvulncheck.com/advisories/justhtml-before-sanitizer-bypass-via-markdown