justhtml before 1.12.0 Sanitizer Bypass via Markdown
Published Aug 23, 2026
9.3
CRITICALCVSS 4.0
EPSS 0.64%
Description
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. <script>) 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 products
-
- Version 0StatusaffectedConstraints<1.12.0
- Version 1.12.0StatusunaffectedConstraints-
- Version
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| EmilStenstrom | Justhtml | unaffected |
|
No data.
No data.
No Red Hat product state for this CVE.
No package ranges for this CVE.
Remediation
No remediation recorded yet.
Metrics
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
1 other source (NVD) ▾
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
No CVSS v3.0 score for this CVE.
No CVSS v2.0 score for this CVE.
This CVE is not in the KEV list.
CISA SSVC (Vulnrichment)
Stakeholder-Specific Vulnerability Categorization from CISA ADP.
Exploitation
PoCAutomatable
YesTechnical Impact
TotalDecision
n/aAssessed Aug 24, 2026 · SSVC 2.0.3
Estimated probability of exploitation in the wild in the next 30 days (FIRST EPSS). As of Oct 3, 2026.
Score over time
Aug–Oct 2026- EPSS v5
Percentile over time
- EPSS v5
Table of values (2 key points)
Flat stretches are collapsed; showing up to 120 newest points.
| Date | Score | Percentile | Model |
|---|---|---|---|
| Oct 3, 2026 | 0.64% (0.00635) | 48.61th | v5 (v2026.06.15) |
| Aug 24, 2026 | 0.38% (0.00381) | 30.81th | v5 (v2026.06.15) |
References (2)
- https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-3rcm-vjrc-p45j exploitvendor-advisory
- https://www.vulncheck.com/advisories/justhtml-before-sanitizer-bypass-via-markdown third-party-advisory
| Link | Providers | Tags |
|---|---|---|
| https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-3rcm-vjrc-p45j | exploitvendor-advisory | |
| https://www.vulncheck.com/advisories/justhtml-before-sanitizer-bypass-via-markdown | third-party-advisory |
Change history (0)
No recorded changes yet.