CVE-2026-8445

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.

CVSS v3 9.8 CRITICAL

9.8^/10

CVSS v3 : CRITICAL

Vector :

Exploitability : 3.9 / Impact : 5.9

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-3rcm-vjrc-p45j
https://www.vulncheck.com/advisories/justhtml-before-sanitizer-bypass-via-markdown
https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-3rcm-vjrc-p45j

Configurations

No configuration.

History

No history.

Information

Published : 2026-08-23 14:16

Updated : 2026-08-26 17:10

NVD link : CVE-2026-8445

Mitre link : CVE-2026-8445

CVE.ORG link : CVE-2026-8445

JSON object : View

Products Affected

No product.

CWE

CWE-79

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

{"id": "CVE-2026-8445", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-8445", "role": "CISA Coordinator", "options": [{"exploitation": "poc"}, {"automatable": "yes"}, {"technicalImpact": "total"}], "version": "2.0.3", "timestamp": "2026-08-24T19:06:10.251827Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "disclosure@vulncheck.com", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 9.8, "attackVector": "NETWORK", "baseSeverity": "CRITICAL", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "integrityImpact": "HIGH", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "NONE", "confidentialityImpact": "HIGH"}, "impactScore": 5.9, "exploitabilityScore": 3.9}], "cvssMetricV40": [{"type": "Secondary", "source": "disclosure@vulncheck.com", "cvssData": {"Safety": "NOT_DEFINED", "version": "4.0", "Recovery": "NOT_DEFINED", "baseScore": 9.3, "Automatable": "NOT_DEFINED", "attackVector": "NETWORK", "baseSeverity": "CRITICAL", "valueDensity": "NOT_DEFINED", "vectorString": "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", "exploitMaturity": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED", "userInteraction": "NONE", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "subIntegrityImpact": "NONE", "vulnIntegrityImpact": "HIGH", "integrityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "vulnAvailabilityImpact": "HIGH", "availabilityRequirement": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "subConfidentialityImpact": "NONE", "vulnConfidentialityImpact": "HIGH", "confidentialityRequirement": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED"}}]}, "affected": [{"source": "disclosure@vulncheck.com", "affectedData": [{"vendor": "EmilStenstrom", "product": "justhtml", "versions": [{"status": "affected", "version": "0", "lessThan": "1.12.0", "versionType": "semver"}, {"status": "unaffected", "version": "1.12.0", "versionType": "semver"}], "packageURL": "pkg:pypi/justhtml", "defaultStatus": "unaffected"}]}], "published": "2026-08-23T14:16:54.957", "references": [{"url": "https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-3rcm-vjrc-p45j", "source": "disclosure@vulncheck.com"}, {"url": "https://www.vulncheck.com/advisories/justhtml-before-sanitizer-bypass-via-markdown", "source": "disclosure@vulncheck.com"}, {"url": "https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-3rcm-vjrc-p45j", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0"}], "vulnStatus": "Deferred", "weaknesses": [{"type": "Secondary", "source": "disclosure@vulncheck.com", "description": [{"lang": "en", "value": "CWE-79"}]}], "descriptions": [{"lang": "en", "value": "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() \u2014 including entity-decoded text (e.g. <script>) or text from RCDATA/RAWTEXT-parsed elements like <title>, <textarea>, <noscript>, and <plaintext> \u2014 can be emitted as raw HTML in the Markdown output, enabling a sanitizer bypass and potential cross-site scripting when that output is rendered."}], "lastModified": "2026-08-26T17:10:53.700", "sourceIdentifier": "disclosure@vulncheck.com"}