Medium
mistune, mistune0 — security advisory
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, the Image directive plugin validates the :width: and :height: options with a regex compiled as _num_re = re.compile(r"^\d+(?:\.\d*)?"). When the validated value is not a plain integer, render_block_image() inserts it directly into a style="width:...;" or style="height:...;" attribute. Because the value was accepted by the prefix-only regex, any CSS after the leading digits reaches the style= attribute verbatim and without escaping. This vulnerability is fixed in 3.2.1.
- 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-2026-44899
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 02:13 UTC · Revision 1
Source evidence
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, the Image directive plugin validates the :width: and :height: options with a regex compiled as _num_re = re.compile(r"^\d+(?:\.\d*)?"). When the validated value is not a plain integer, render_block_image() inserts it directly into a style="width:...;" or style="height:...;" attribute. Because the value was accepted by the prefix-only regex, any CSS after the leading digits reaches the style= attribute verbatim and without escaping. This vulnerability is fixed in 3.2.1.
osv:UBUNTU-CVE-2026-44899
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": "73a18324cf05c6a4b0de089045d2cbc0147a1a8c0ac3b01ca777a4db6aee59fd",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-44899",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "UBUNTU-CVE-2026-44899",
"summary": "Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, the Image directive plugin validates the :width: and :height: options with a regex compiled as _num_re = re.compile(r\"^\\d+(?:\\.\\d*)?\"). When the validated value is not a plain integer, render_block_image() inserts it directly into a style=\"width:...;\" or style=\"height:...;\" attribute. Because the value was accepted by the prefix-only regex, any CSS after the leading digits reaches the style= attribute verbatim and without escaping. This vulnerability is fixed in 3.2.1.",
"evidence": "osv:UBUNTU-CVE-2026-44899",
"products": [
{
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"evidence": "/affected/0/package/name"
},
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"evidence": "/affected/0/versions"
},
{
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}
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},
{
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{
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{
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"evidence": "/affected/8/versions"
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{
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]
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{
"name": {
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{
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{
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{
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],
"severity": "medium",
"structured": {
"id": "UBUNTU-CVE-2026-44899",
"aliases": [
"UBUNTU-CVE-2026-44899"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N"
},
{
"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": [
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"events": [
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}
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"ecosystem": "Ubuntu:16.04:LTS"
},
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],
"database_specific": {
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},
"ecosystem_specific": {
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},
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],
"modified": "2026-10-17T12:58:21.837324191Z",
"provider": "osv",
"upstream": [
"CVE-2026-44899"
],
"references": [
"https://ubuntu.com/security/CVE-2026-44899",
"https://www.cve.org/CVERecord?id=CVE-2026-44899",
"https://github.com/lepture/mistune/releases/tag/v3.2.1",
"https://github.com/lepture/mistune/security/advisories/GHSA-ccfx-mfmx-2fx9"
]
},
"related_cves": [
{
"value": "CVE-2026-44899",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/1/score"
},
"source_id": "core-osv",
"document_id": 358600,
"published_at": "2026-05-26T21:16:00+00:00"
}