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Discourse CVE-2026-72728

| EUVDEUVD-2026-55667 MEDIUM
Improper Input Validation (CWE-20)
2026-08-10 GitHub_M
Authentication Bypass Discourse
6.3
CVSS 3.1 · Vendor: GitHub_M
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Severity by source

Vendor (GitHub_M) PRIMARY
6.3 MEDIUM
AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
vuln.today AI
5.4 MEDIUM

Network-reachable via authenticated users (PR:L, AV:N); content injection yields limited confidentiality and integrity impact; no availability impact is substantiated by the iframe injection mechanism described.

3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
Low

Lifecycle Timeline

3
Patch available
Aug 10, 2026 - 17:03 EUVD
Source Code Evidence Fetched
Aug 10, 2026 - 16:53 vuln.today
Analysis Generated
Aug 10, 2026 - 16:53 vuln.today

DescriptionCVE.org

Discourse is an open-source discussion platform. Prior to 2026.1.7, an authenticated user could submit specially formed URLs that bypassed the Onebox allowlist and embedded malicious content in a site. This issue is fixed in versions 2026.1.7, 2026.6.2, 2026.7.1, and 2026.8.0-latest.1.

AnalysisAI

Onebox allowlist bypass in Discourse (all versions prior to 2026.1.7) enables authenticated forum users to embed malicious iframes and attacker-controlled content in posts by exploiting a regex prefix-matching flaw in the origins_to_regexes method. The core defect - missing URL boundary anchors and an overly permissive wildcard expansion - allows domains like youtube.com.attacker.example to pass validation as the allowlisted youtube.com. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Vulnerability AssessmentAI

Exploitation Exploitation requires an authenticated Discourse account with sufficient trust level to create posts that trigger Onebox resolution (Trust Level 0 or above by default, though site administrators may restrict this to higher trust levels). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 3.1 vector (AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L, score 6.3) categorizes this as medium severity: network-reachable, low complexity, requiring only an authenticated account, with no user interaction and unchanged scope. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Upgrade Discourse to version 2026.1.7, 2026.6.2, 2026.7.1, or 2026.8.0-latest.1 as confirmed by the GitHub Security Advisory (https://github.com/discourse/discourse/security/advisories/GHSA-qp9j-3v7r-wrvr) and the upstream fix commit (https://github.com/discourse/discourse/commit/92eec47e8b477cb8b4ccdb237e26dc1ba8f8b76b). … Detailed patch versions, workarounds, and compensating controls in full report.
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Same weakness CWE-20 – Improper Input Validation

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CVE-2026-72728 vulnerability details – vuln.today
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