CVE-2026-5388 (GCVE-0-2026-5388)
Vulnerability from cvelistv5 – Published: 2026-08-23 13:34 – Updated: 2026-08-26 16:16
VLAI
EPSS
VEX
Title
justhtml before 1.15.0 Multiple Security Issues
Summary
justhtml before 1.15.0 contains multiple security issues in URL sanitization helpers (clean_url_value/clean_url_in_js_string), HTML serialization, Markdown passthrough (html_passthrough=True), and several custom sanitization-policy edge cases. Depending on configuration, an attacker can bypass sanitization to inject active HTML and JavaScript — for example via encoded javascript: URLs, backslash-based relative URLs resolved as remote hosts, markup-breaking programmatic element/attribute names or HTML comments, raw </textarea> reintroduction through Markdown passthrough, or preserved <style>/<meta http-equiv=refresh>/<base href> tags in custom policies. Most custom-policy issues do not affect the default sanitize=True configuration; they primarily affect helper APIs, programmatic DOM construction, html_passthrough=True, and custom policies/transform pipelines.
Severity
9.8 (Critical)
SSVC
Exploitation: none
Automatable: yes
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-26 16:07 UTC
CWE
- CWE-20 - Improper Input Validation
Assigner
References
2 references
| URL | Tags |
|---|---|
| https://github.com/EmilStenstrom/justhtml/securit… | vendor-advisory |
| https://www.vulncheck.com/advisories/justhtml-bef… | third-party-advisory |
Impacted products
1 product
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| EmilStenstrom | justhtml |
Affected:
0 , < 1.15.0
(semver)
Unaffected: 1.15.0 (semver) |
guessed |
Date Public
2026-04-09 00:00
{
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-5388",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "yes"
},
{
"Technical Impact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-08-26T16:07:56.131062Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-08-26T16:16:10.959Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"packageURL": "pkg:pypi/justhtml",
"product": "justhtml",
"vendor": "EmilStenstrom",
"versions": [
{
"lessThan": "1.15.0",
"status": "affected",
"version": "0",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "1.15.0",
"versionType": "semver"
}
]
}
],
"credits": [
{
"lang": "en",
"type": "coordinator",
"value": "EmilStenstrom"
}
],
"datePublic": "2026-04-09T00:00:00.000Z",
"descriptions": [
{
"lang": "en",
"value": "justhtml before 1.15.0 contains multiple security issues in URL sanitization helpers (clean_url_value/clean_url_in_js_string), HTML serialization, Markdown passthrough (html_passthrough=True), and several custom sanitization-policy edge cases. Depending on configuration, an attacker can bypass sanitization to inject active HTML and JavaScript \u2014 for example via encoded javascript: URLs, backslash-based relative URLs resolved as remote hosts, markup-breaking programmatic element/attribute names or HTML comments, raw \u003c/textarea\u003e reintroduction through Markdown passthrough, or preserved \u003cstyle\u003e/\u003cmeta http-equiv=refresh\u003e/\u003cbase href\u003e tags in custom policies. Most custom-policy issues do not affect the default sanitize=True configuration; they primarily affect helper APIs, programmatic DOM construction, html_passthrough=True, and custom policies/transform pipelines."
}
],
"metrics": [
{
"cvssV4_0": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "NONE",
"attackVector": "NETWORK",
"baseScore": 9.3,
"baseSeverity": "CRITICAL",
"exploitMaturity": "NOT_DEFINED",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "NONE",
"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",
"version": "4.0",
"vulnAvailabilityImpact": "HIGH",
"vulnConfidentialityImpact": "HIGH",
"vulnIntegrityImpact": "HIGH",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS"
},
{
"cvssV3_1": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "HIGH",
"baseScore": 9.8,
"baseSeverity": "CRITICAL",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"format": "CVSS"
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-20",
"description": "Improper Input Validation",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-23T13:34:09.169Z",
"orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
"shortName": "VulnCheck"
},
"references": [
{
"name": "GitHub Security Advisory (GHSA-c9vm-hv86-f23r)",
"tags": [
"vendor-advisory"
],
"url": "https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-c9vm-hv86-f23r"
},
{
"name": "VulnCheck Advisory: justhtml before 1.15.0 Multiple Security Issues",
"tags": [
"third-party-advisory"
],
"url": "https://www.vulncheck.com/advisories/justhtml-before-multiple-security-issues"
}
],
"title": "justhtml before 1.15.0 Multiple Security Issues",
"x_generator": {
"engine": "vulncheck-endgame"
}
}
},
"cveMetadata": {
"assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
"assignerShortName": "VulnCheck",
"cveId": "CVE-2026-5388",
"datePublished": "2026-08-23T13:34:09.169Z",
"dateReserved": "2026-04-01T21:11:10.753Z",
"dateUpdated": "2026-08-26T16:16:10.959Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"epss": {
"cve": "CVE-2026-5388",
"date": "2026-09-26",
"epss": "0.00587",
"percentile": "0.45885"
},
"nvd": {
"cve": {
"affected": [
{
"affectedData": [
{
"defaultStatus": "unaffected",
"packageURL": "pkg:pypi/justhtml",
"product": "justhtml",
"vendor": "EmilStenstrom",
"versions": [
{
"lessThan": "1.15.0",
"status": "affected",
"version": "0",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "1.15.0",
"versionType": "semver"
}
]
}
],
"source": "disclosure@vulncheck.com"
}
],
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "justhtml before 1.15.0 contains multiple security issues in URL sanitization helpers (clean_url_value/clean_url_in_js_string), HTML serialization, Markdown passthrough (html_passthrough=True), and several custom sanitization-policy edge cases. Depending on configuration, an attacker can bypass sanitization to inject active HTML and JavaScript \u2014 for example via encoded javascript: URLs, backslash-based relative URLs resolved as remote hosts, markup-breaking programmatic element/attribute names or HTML comments, raw \u003c/textarea\u003e reintroduction through Markdown passthrough, or preserved \u003cstyle\u003e/\u003cmeta http-equiv=refresh\u003e/\u003cbase href\u003e tags in custom policies. Most custom-policy issues do not affect the default sanitize=True configuration; they primarily affect helper APIs, programmatic DOM construction, html_passthrough=True, and custom policies/transform pipelines."
}
],
"id": "CVE-2026-5388",
"lastModified": "2026-08-26T17:17:09.040",
"metrics": {
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "HIGH",
"baseScore": 9.8,
"baseSeverity": "CRITICAL",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"exploitabilityScore": 3.9,
"impactScore": 5.9,
"source": "disclosure@vulncheck.com",
"type": "Secondary"
}
],
"cvssMetricV40": [
{
"cvssData": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "NONE",
"attackVector": "NETWORK",
"availabilityRequirement": "NOT_DEFINED",
"baseScore": 9.3,
"baseSeverity": "CRITICAL",
"confidentialityRequirement": "NOT_DEFINED",
"exploitMaturity": "NOT_DEFINED",
"integrityRequirement": "NOT_DEFINED",
"modifiedAttackComplexity": "NOT_DEFINED",
"modifiedAttackRequirements": "NOT_DEFINED",
"modifiedAttackVector": "NOT_DEFINED",
"modifiedPrivilegesRequired": "NOT_DEFINED",
"modifiedSubAvailabilityImpact": "NOT_DEFINED",
"modifiedSubConfidentialityImpact": "NOT_DEFINED",
"modifiedSubIntegrityImpact": "NOT_DEFINED",
"modifiedUserInteraction": "NOT_DEFINED",
"modifiedVulnAvailabilityImpact": "NOT_DEFINED",
"modifiedVulnConfidentialityImpact": "NOT_DEFINED",
"modifiedVulnIntegrityImpact": "NOT_DEFINED",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "NONE",
"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",
"version": "4.0",
"vulnAvailabilityImpact": "HIGH",
"vulnConfidentialityImpact": "HIGH",
"vulnIntegrityImpact": "HIGH",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"source": "disclosure@vulncheck.com",
"type": "Secondary"
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"id": "CVE-2026-5388",
"options": [
{
"exploitation": "none"
},
{
"automatable": "yes"
},
{
"technicalImpact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-08-26T16:07:56.131062Z",
"version": "2.0.3"
}
}
]
},
"published": "2026-08-23T14:16:53.470",
"references": [
{
"source": "disclosure@vulncheck.com",
"url": "https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-c9vm-hv86-f23r"
},
{
"source": "disclosure@vulncheck.com",
"url": "https://www.vulncheck.com/advisories/justhtml-before-multiple-security-issues"
}
],
"sourceIdentifier": "disclosure@vulncheck.com",
"vulnStatus": "Deferred",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-20"
}
],
"source": "disclosure@vulncheck.com",
"type": "Secondary"
}
]
}
},
"vulnrichment": {
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-5388",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "yes"
},
{
"Technical Impact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-08-26T16:07:56.131062Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-08-26T16:07:57.635Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"packageURL": "pkg:pypi/justhtml",
"product": "justhtml",
"vendor": "EmilStenstrom",
"versions": [
{
"lessThan": "1.15.0",
"status": "affected",
"version": "0",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "1.15.0",
"versionType": "semver"
}
]
}
],
"credits": [
{
"lang": "en",
"type": "coordinator",
"value": "EmilStenstrom"
}
],
"datePublic": "2026-04-09T00:00:00.000Z",
"descriptions": [
{
"lang": "en",
"value": "justhtml before 1.15.0 contains multiple security issues in URL sanitization helpers (clean_url_value/clean_url_in_js_string), HTML serialization, Markdown passthrough (html_passthrough=True), and several custom sanitization-policy edge cases. Depending on configuration, an attacker can bypass sanitization to inject active HTML and JavaScript \u2014 for example via encoded javascript: URLs, backslash-based relative URLs resolved as remote hosts, markup-breaking programmatic element/attribute names or HTML comments, raw \u003c/textarea\u003e reintroduction through Markdown passthrough, or preserved \u003cstyle\u003e/\u003cmeta http-equiv=refresh\u003e/\u003cbase href\u003e tags in custom policies. Most custom-policy issues do not affect the default sanitize=True configuration; they primarily affect helper APIs, programmatic DOM construction, html_passthrough=True, and custom policies/transform pipelines."
}
],
"metrics": [
{
"cvssV4_0": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "NONE",
"attackVector": "NETWORK",
"baseScore": 9.3,
"baseSeverity": "CRITICAL",
"exploitMaturity": "NOT_DEFINED",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "NONE",
"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",
"version": "4.0",
"vulnAvailabilityImpact": "HIGH",
"vulnConfidentialityImpact": "HIGH",
"vulnIntegrityImpact": "HIGH",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS"
},
{
"cvssV3_1": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "HIGH",
"baseScore": 9.8,
"baseSeverity": "CRITICAL",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"format": "CVSS"
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-20",
"description": "Improper Input Validation",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-23T13:34:09.169Z",
"orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
"shortName": "VulnCheck"
},
"references": [
{
"name": "GitHub Security Advisory (GHSA-c9vm-hv86-f23r)",
"tags": [
"vendor-advisory"
],
"url": "https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-c9vm-hv86-f23r"
},
{
"name": "VulnCheck Advisory: justhtml before 1.15.0 Multiple Security Issues",
"tags": [
"third-party-advisory"
],
"url": "https://www.vulncheck.com/advisories/justhtml-before-multiple-security-issues"
}
],
"title": "justhtml before 1.15.0 Multiple Security Issues",
"x_generator": {
"engine": "vulncheck-endgame"
}
}
},
"cveMetadata": {
"assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
"assignerShortName": "VulnCheck",
"cveId": "CVE-2026-5388",
"datePublished": "2026-08-23T13:34:09.169Z",
"dateReserved": "2026-04-01T21:11:10.753Z",
"dateUpdated": "2026-08-26T16:16:10.959Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
Loading…
Loading…
Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Loading…
Loading…
The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
Loading…
Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
Loading…