Medium
Discourse: Onebox Domain Blocklist Bypass via Case-Sensitive Comparison
Type: advisorySources: OSV
Discourse is an open-source discussion platform. Prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0, Onebox::DomainChecker.is_blocked? compares hostnames and SiteSetting.blocked_onebox_domains entries case-sensitively, allowing an attacker to bypass configured Onebox domain restrictions by changing character casing in a redirect target hostname. This issue is fixed in versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-72721
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 3 Nov 2026, 11:01 UTC · Revision 1
Source evidence
Discourse: Onebox Domain Blocklist Bypass via Case-Sensitive Comparison
core-osv · Original sourcePublished 10 Aug 2026, 15:48 UTC
Discourse is an open-source discussion platform. Prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0, Onebox::DomainChecker.is_blocked? compares hostnames and SiteSetting.blocked_onebox_domains entries case-sensitively, allowing an attacker to bypass configured Onebox domain restrictions by changing character casing in a redirect target hostname. This issue is fixed in versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0.
osv:CVE-2026-72721
Complete source record
{
"id": "0a77f4659e72240d1d61c52c5d65948b5c9e67525d610ef7ea77a2db491ffa95",
"url": "https://osv.dev/vulnerability/CVE-2026-72721",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "Discourse: Onebox Domain Blocklist Bypass via Case-Sensitive Comparison",
"summary": "Discourse is an open-source discussion platform. Prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0, Onebox::DomainChecker.is_blocked? compares hostnames and SiteSetting.blocked_onebox_domains entries case-sensitively, allowing an attacker to bypass configured Onebox domain restrictions by changing character casing in a redirect target hostname. This issue is fixed in versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0.",
"evidence": "osv:CVE-2026-72721",
"products": [],
"severity": "medium",
"structured": {
"id": "CVE-2026-72721",
"aliases": [
"BIT-discourse-2026-72721",
"CVE-2026-72721",
"GHSA-3x7x-24rq-h5j6"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/discourse/discourse",
"type": "GIT",
"events": [
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"introduced": "0"
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{
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{
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"database_specific": {
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{
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"source": "AFFECTED_FIELD",
"strategy": "StringRangeExpression"
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{
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"source": "REFERENCES_COMMIT"
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{
"range": [
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"source": "REFERENCES_COMMIT"
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}
}
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"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-72721.json"
}
}
],
"modified": "2026-10-28T02:30:28.063566884Z",
"provider": "osv",
"references": [
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72721.json",
"https://github.com/discourse/discourse/security/advisories/GHSA-3x7x-24rq-h5j6",
"https://nvd.nist.gov/vuln/detail/CVE-2026-72721",
"https://github.com/discourse/discourse/commit/a3e10759fef47f03d450649bb51d9e84f4c68b8f",
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"https://github.com/discourse/discourse/pull/42093",
"https://github.com/discourse/discourse/pull/42094"
],
"provider_metadata": {
"cwe_ids": [
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],
"cna_assigner": "GitHub_M",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72721.json"
}
},
"related_cves": [
{
"value": "CVE-2026-72721",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 494808,
"published_at": "2026-08-10T15:48:30.548+00:00"
}