Medium
commonmark, markdown — security advisory
league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 1.5.0 until 2.9.0, the AttributesExtension's href and src unsafe-link filter can be bypassed by embedding control bytes, such as a tab, carriage return, line feed, or leading C0 control character, in a javascript: URL that browsers discard before parsing the scheme, causing the browser to still execute the script even when the unsafe-link filter is enabled. This issue is fixed in 2.9.0.
- Products
- commonmark, markdown
- Affected versions
- 0.9.1-3, 0.9.1-4, 0.9.1-5, 0.9.1-8, 0.9.1-8build1, 1.0.1-10, 1.0.1-10.1, 1.0.1-12, 1.0.1-14, 1.0.1-7, 1.0.1-8, 1.0.1-9
- Fixed versions
- Not specified
- CVEs
- CVE-2026-71478
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 03:14 UTC · Revision 1
Source evidence
league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 1.5.0 until 2.9.0, the AttributesExtension's href and src unsafe-link filter can be bypassed by embedding control bytes, such as a tab, carriage return, line feed, or leading C0 control character, in a javascript: URL that browsers discard before parsing the scheme, causing the browser to still execute the script even when the unsafe-link filter is enabled. This issue is fixed in 2.9.0.
osv:UBUNTU-CVE-2026-71478
markdown
Fixed versions: Not specified
markdown
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markdown
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commonmark
Fixed versions: Not specified
markdown
Fixed versions: Not specified
commonmark
Fixed versions: Not specified
markdown
Fixed versions: Not specified
commonmark
Fixed versions: Not specified
markdown
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commonmark
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markdown
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Complete source record
{
"id": "7f00d1e938c364aa381012c5beac129e7dcca2cf06d7f0cb3b45d395daf8a1f9",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-71478",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "UBUNTU-CVE-2026-71478",
"summary": "league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 1.5.0 until 2.9.0, the AttributesExtension's href and src unsafe-link filter can be bypassed by embedding control bytes, such as a tab, carriage return, line feed, or leading C0 control character, in a javascript: URL that browsers discard before parsing the scheme, causing the browser to still execute the script even when the unsafe-link filter is enabled. This issue is fixed in 2.9.0.",
"evidence": "osv:UBUNTU-CVE-2026-71478",
"products": [
{
"name": {
"value": "markdown",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "1.0.1-7",
"evidence": "/affected/0/versions"
},
{
"value": "1.0.1-8",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "markdown",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "1.0.1-9",
"evidence": "/affected/1/versions"
},
{
"value": "1.0.1-10",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
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"evidence": "/affected/2/package/name"
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{
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"affected_versions": [
{
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}
]
},
{
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"evidence": "/affected/4/package/name"
},
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"affected_versions": [
{
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"evidence": "/affected/4/versions"
}
]
},
{
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},
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{
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"evidence": "/affected/5/versions"
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{
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}
]
},
{
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},
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{
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"evidence": "/affected/6/versions"
}
]
},
{
"name": {
"value": "commonmark",
"evidence": "/affected/7/package/name"
},
"prerequisites": [],
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"affected_versions": [
{
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}
]
},
{
"name": {
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"evidence": "/affected/8/package/name"
},
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{
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]
},
{
"name": {
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},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "0.9.1-8",
"evidence": "/affected/9/versions"
},
{
"value": "0.9.1-8build1",
"evidence": "/affected/9/versions"
}
]
},
{
"name": {
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"evidence": "/affected/10/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "1.0.1-14",
"evidence": "/affected/10/versions"
}
]
}
],
"severity": "medium",
"structured": {
"id": "UBUNTU-CVE-2026-71478",
"aliases": [
"UBUNTU-CVE-2026-71478"
],
"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"
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]
}
],
"package": {
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},
"versions": [
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"1.0.1-8"
],
"database_specific": {
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},
"ecosystem_specific": {
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{
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],
"package": {
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"ecosystem": "Ubuntu:18.04:LTS"
},
"versions": [
"1.0.1-9",
"1.0.1-10"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71478.json"
},
"ecosystem_specific": {
"binaries": [
{
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}
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}
},
{
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"events": [
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],
"package": {
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"purl": "pkg:deb/ubuntu/markdown?arch=source&distro=focal",
"ecosystem": "Ubuntu:20.04:LTS"
},
"versions": [
"1.0.1-10"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71478.json"
},
"ecosystem_specific": {
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"binary_version": "1.0.1-10"
}
]
}
},
{
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],
"package": {
"name": "commonmark",
"purl": "pkg:deb/ubuntu/commonmark?arch=source&distro=jammy",
"ecosystem": "Ubuntu:22.04:LTS"
},
"versions": [
"0.9.1-3"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71478.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "python3-commonmark",
"binary_version": "0.9.1-3"
}
]
}
},
{
"ranges": [
{
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],
"package": {
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"purl": "pkg:deb/ubuntu/markdown?arch=source&distro=jammy",
"ecosystem": "Ubuntu:22.04:LTS"
},
"versions": [
"1.0.1-10.1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71478.json"
},
"ecosystem_specific": {
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}
]
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{
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],
"package": {
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"purl": "pkg:deb/ubuntu/commonmark?arch=source&distro=noble",
"ecosystem": "Ubuntu:24.04:LTS"
},
"versions": [
"0.9.1-4",
"0.9.1-5"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71478.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "python3-commonmark",
"binary_version": "0.9.1-5"
}
]
}
},
{
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"versions": [
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],
"database_specific": {
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},
"versions": [
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],
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],
"modified": "2026-10-17T13:00:44.815170484Z",
"provider": "osv",
"upstream": [
"CVE-2026-71478"
],
"references": [
"https://ubuntu.com/security/CVE-2026-71478",
"https://www.cve.org/CVERecord?id=CVE-2026-71478",
"https://github.com/thephpleague/commonmark/commit/493a5aa7d65754b73846006eaff9c2c4431a8e2c",
"https://github.com/thephpleague/commonmark/releases/tag/2.9.0",
"https://github.com/thephpleague/commonmark/security/advisories/GHSA-29pj-957v-52mc"
]
},
"related_cves": [
{
"value": "CVE-2026-71478",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 360808,
"published_at": "2026-08-06T22:18:00+00:00"
}