Medium
mistune, mistune0 — security advisory
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_toc_ul() builds a table-of-contents tree from a list of (level, id, text) tuples. Both the id value (used as href="#") and the text value (used as the visible link label) are inserted into tags via a plain Python format string — with no HTML escaping applied to either value. When heading IDs are derived from user-supplied heading text (the standard use-case for readable slug anchors), an attacker can craft a heading whose text breaks out of the href="#..." attribute context, injecting arbitrary HTML tags including
- Products
- mistune, mistune0
- Affected versions
- 0.6-2, 0.7.1-1, 0.7.4-1, 0.8-1, 0.8.1-1, 0.8.3-2, 0.8.4-1, 0.8.4-2, 0.8.4-4, 0.8.4-5, 0.8.4-6, 2.0.0-1+really0.8.4-1, 2.0.4-2, 3.0.2-1, 3.0.2-2, 3.1.3-1, 3.1.4-1
- Fixed versions
- Not specified
- CVEs
- CVE-2026-44898
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 03:04 UTC · Revision 1
Source evidence
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_toc_ul() builds a table-of-contents tree from a list of (level, id, text) tuples. Both the id value (used as href="#") and the text value (used as the visible link label) are inserted into tags via a plain Python format string — with no HTML escaping applied to either value. When heading IDs are derived from user-supplied heading text (the standard use-case for readable slug anchors), an attacker can craft a heading whose text breaks out of the href="#..." attribute context, injecting arbitrary HTML tags including
osv:UBUNTU-CVE-2026-44898
mistune
Fixed versions: Not specified
mistune
Fixed versions: Not specified
mistune
Fixed versions: Not specified
mistune
Fixed versions: Not specified
mistune0
Fixed versions: Not specified
mistune
Fixed versions: Not specified
mistune0
Fixed versions: Not specified
mistune
Fixed versions: Not specified
mistune0
Fixed versions: Not specified
mistune
Fixed versions: Not specified
mistune0
Fixed versions: Not specified
mistune
Fixed versions: Not specified
mistune0
Fixed versions: Not specified
Complete source record
{
"id": "9656caf0b27041c8a9c228c1df8c34c2245f505f29d215b09f475a595a5f8c53",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-44898",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "UBUNTU-CVE-2026-44898",
"summary": "Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_toc_ul() builds a table-of-contents tree from a list of (level, id, text) tuples. Both the id value (used as href=\"#\") and the text value (used as the visible link label) are inserted into tags via a plain Python format string — with no HTML escaping applied to either value. When heading IDs are derived from user-supplied heading text (the standard use-case for readable slug anchors), an attacker can craft a heading whose text breaks out of the href=\"#...\" attribute context, injecting arbitrary HTML tags including",
"evidence": "osv:UBUNTU-CVE-2026-44898",
"products": [
{
"name": {
"value": "mistune",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "0.6-2",
"evidence": "/affected/0/versions"
},
{
"value": "0.7.1-1",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "mistune",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "0.7.4-1",
"evidence": "/affected/1/versions"
},
{
"value": "0.8-1",
"evidence": "/affected/1/versions"
},
{
"value": "0.8.1-1",
"evidence": "/affected/1/versions"
},
{
"value": "0.8.3-2",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
"value": "mistune",
"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "0.8.4-1",
"evidence": "/affected/2/versions"
},
{
"value": "0.8.4-2",
"evidence": "/affected/2/versions"
}
]
},
{
"name": {
"value": "mistune",
"evidence": "/affected/3/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "0.8.4-4",
"evidence": "/affected/3/versions"
},
{
"value": "0.8.4-5",
"evidence": "/affected/3/versions"
},
{
"value": "2.0.0-1+really0.8.4-1",
"evidence": "/affected/3/versions"
}
]
},
{
"name": {
"value": "mistune0",
"evidence": "/affected/4/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "0.8.4-1",
"evidence": "/affected/4/versions"
},
{
"value": "0.8.4-2",
"evidence": "/affected/4/versions"
}
]
},
{
"name": {
"value": "mistune",
"evidence": "/affected/5/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "2.0.4-2",
"evidence": "/affected/5/versions"
},
{
"value": "3.0.2-1",
"evidence": "/affected/5/versions"
}
]
},
{
"name": {
"value": "mistune0",
"evidence": "/affected/6/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "0.8.4-2",
"evidence": "/affected/6/versions"
}
]
},
{
"name": {
"value": "mistune",
"evidence": "/affected/7/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.0.2-2",
"evidence": "/affected/7/versions"
},
{
"value": "3.1.3-1",
"evidence": "/affected/7/versions"
}
]
},
{
"name": {
"value": "mistune0",
"evidence": "/affected/8/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "0.8.4-4",
"evidence": "/affected/8/versions"
}
]
},
{
"name": {
"value": "mistune",
"evidence": "/affected/9/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.1.4-1",
"evidence": "/affected/9/versions"
}
]
},
{
"name": {
"value": "mistune0",
"evidence": "/affected/10/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "0.8.4-6",
"evidence": "/affected/10/versions"
}
]
},
{
"name": {
"value": "mistune",
"evidence": "/affected/11/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.1.3-1",
"evidence": "/affected/11/versions"
},
{
"value": "3.1.4-1",
"evidence": "/affected/11/versions"
}
]
},
{
"name": {
"value": "mistune0",
"evidence": "/affected/12/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "0.8.4-4",
"evidence": "/affected/12/versions"
},
{
"value": "0.8.4-5",
"evidence": "/affected/12/versions"
},
{
"value": "0.8.4-6",
"evidence": "/affected/12/versions"
}
]
}
],
"severity": "medium",
"structured": {
"id": "UBUNTU-CVE-2026-44898",
"aliases": [
"UBUNTU-CVE-2026-44898"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
},
{
"type": "Ubuntu",
"score": "medium"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "mistune",
"purl": "pkg:deb/ubuntu/mistune?arch=source&distro=xenial",
"ecosystem": "Ubuntu:16.04:LTS"
},
"versions": [
"0.6-2",
"0.7.1-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-44898.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "python-mistune",
"binary_version": "0.7.1-1"
},
{
"binary_name": "python3-mistune",
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"purl": "pkg:deb/ubuntu/mistune?arch=source&distro=bionic",
"ecosystem": "Ubuntu:18.04:LTS"
},
"versions": [
"0.7.4-1",
"0.8-1",
"0.8.1-1",
"0.8.3-2"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-44898.json"
},
"ecosystem_specific": {
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"binary_name": "python-mistune",
"binary_version": "0.8.3-2"
},
{
"binary_name": "python3-mistune",
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}
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{
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"name": "mistune",
"purl": "pkg:deb/ubuntu/mistune?arch=source&distro=focal",
"ecosystem": "Ubuntu:20.04:LTS"
},
"versions": [
"0.8.4-1",
"0.8.4-2"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-44898.json"
},
"ecosystem_specific": {
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}
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}
},
{
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}
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}
],
"package": {
"name": "mistune",
"purl": "pkg:deb/ubuntu/mistune?arch=source&distro=jammy",
"ecosystem": "Ubuntu:22.04:LTS"
},
"versions": [
"0.8.4-4",
"0.8.4-5",
"2.0.0-1+really0.8.4-1"
],
"database_specific": {
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},
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{
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"purl": "pkg:deb/ubuntu/mistune0?arch=source&distro=jammy",
"ecosystem": "Ubuntu:22.04:LTS"
},
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],
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},
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"3.0.2-1"
],
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},
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"3.1.3-1"
],
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},
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},
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],
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},
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},
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],
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"ecosystem": "Ubuntu:26.04:LTS"
},
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"3.1.3-1",
"3.1.4-1"
],
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},
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],
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"purl": "pkg:deb/ubuntu/mistune0?arch=source&distro=resolute",
"ecosystem": "Ubuntu:26.04:LTS"
},
"versions": [
"0.8.4-4",
"0.8.4-5",
"0.8.4-6"
],
"database_specific": {
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},
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{
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}
],
"modified": "2026-10-17T13:00:09.833090233Z",
"provider": "osv",
"upstream": [
"CVE-2026-44898"
],
"references": [
"https://ubuntu.com/security/CVE-2026-44898",
"https://www.cve.org/CVERecord?id=CVE-2026-44898",
"https://github.com/lepture/mistune/releases/tag/v3.2.1",
"https://github.com/lepture/mistune/security/advisories/GHSA-6269-cqxg-mhhv"
]
},
"related_cves": [
{
"value": "CVE-2026-44898",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 360377,
"published_at": "2026-05-26T21:16:00+00:00"
}