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CVE-2026-72721— Discourse: Onebox Domain Blocklist Bypass via Case-Sensitive Comparison

Quick assessment

Affected
discourse discourse
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Discourse是Discourse社区开源的一个集成人工智能技术的论坛社区平台。 Discourse 2026.1.6之前版本、2026.5.2之前版本、2026.6.1之前版本和2026.7.0之前版本存在输入验证错误漏洞，该漏洞源于Onebox::DomainChecker.is_blocked?函数对主机名和blocked_onebox_domains条目的比较区分大小写，可能允许攻击者通过更改重定向目标主机名的大小写绕过配置的Onebox域名限制。

CVSS 5.3 · Medium EPSS 0.58% · P47

Affected Version Matrix 4

VendorProduct Version RangeStatus
discourse discourse < 2026.1.6 affected
>= 2026.5.0-latest, < 2026.5.2 affected
>= 2026.6.0-latest, < 2026.6.1 affected
>= 2026.7.0-latest, < 2026.7.0 affected
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I. Basic Information for CVE-2026-72721

Vulnerability Information
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Vulnerability Title
Discourse: Onebox Domain Blocklist Bypass via Case-Sensitive Comparison
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
大小写敏感处理不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Discourse 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Discourse是Discourse社区开源的一个集成人工智能技术的论坛社区平台。 Discourse 2026.1.6之前版本、2026.5.2之前版本、2026.6.1之前版本和2026.7.0之前版本存在输入验证错误漏洞，该漏洞源于Onebox::DomainChecker.is_blocked?函数对主机名和blocked_onebox_domains条目的比较区分大小写，可能允许攻击者通过更改重定向目标主机名的大小写绕过配置的Onebox域名限制。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
discourse discourse < 2026.1.6 -

II. Public POCs for CVE-2026-72721

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III. Intelligence Information for CVE-2026-72721

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Patches & Fixes for CVE-2026-72721 (8)

Vendor Advisories for CVE-2026-72721 (1)

Same Patch Batch · discourse · 2026-08-10 · 13 CVEs total

CVE-2026-72730 8.7 HIGH Discourse: Stored XSS chat-transcript username unescaped in Rich Text Editor
CVE-2026-72731 7.1 HIGH Discourse: Strip SQL comments and use non-recursive parameter interpolation in Data Explor
CVE-2026-72726 6.5 MEDIUM Discourse: Unauthorized eavesdropping on private AI bot conversations.
CVE-2026-72720 6.4 MEDIUM Discourse: HTML injection in PrettyText.format_for_email from cooked-attribute reparsing
CVE-2026-72728 6.3 MEDIUM Discourse: Onebox iframe origin allowlist enforces URL authority boundary
CVE-2026-72725 5.4 MEDIUM Discourse: Stored XSS in staff action logs injects staff UI
CVE-2026-72723 5.3 MEDIUM Discourse: Anonymous sidebar serialization exposes descriptions of category-restricted tag
CVE-2026-72727 4.8 MEDIUM Discourse: Stored XSS in the moderation review queue
CVE-2026-72722 4.3 MEDIUM Discourse: Duplicate lookup reveals restricted topic titles through canonicalized URLs
CVE-2026-72724 4.3 MEDIUM Discourse: Private Chat Threat Message Disclosure via Chat Onebox Channel/Threat ID Mismat
CVE-2026-72732 4.3 MEDIUM Discourse: Templates endpoint exposes hidden tag names
CVE-2026-72729 2.0 LOW Discourse: Stored XSS in discourse-local-dates plugin

IV. Related Vulnerabilities

Same product: discourse
Same vendor: discourse
Same weakness: CWE-178

V. Comments for CVE-2026-72721

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