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Discourse EUVDEUVD-2026-42737

| CVE-2026-59828 MEDIUM
Information Exposure (CWE-200)
2026-07-09 security-advisories@github.com
Information Disclosure Discourse
5.3
CVSS 3.1 · Vendor: github
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Severity by source

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

Network-exploitable without authentication or user interaction; impact limited to partial confidentiality loss of hidden revision content with no integrity or availability effect.

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

Primary rating from Vendor (github).

CVSS VectorVendor: github

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

Lifecycle Timeline

2
Patch available
Jul 09, 2026 - 23:02 EUVD
Analysis Generated
Jul 09, 2026 - 22:48 vuln.today

DescriptionCVE.org

Discourse is an open-source discussion platform. Prior to 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, post revisions that should be hidden from regular users could be leaked through visible diffs on adjacent revisions serialized by PostRevisionSerializer. This issue is fixed in versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5.

AnalysisAI

Discourse's post revision system exposes hidden edit history to unauthenticated network users through a serialization flaw in PostRevisionSerializer. When computing diffs between adjacent visible revisions, the serializer failed to enforce visibility restrictions, leaking content from revisions that moderators or administrators had marked as hidden. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Browse public Discourse forum
Delivery
Identify post with revision history
Exploit
Request revision diff via API or UI
Execution
PostRevisionSerializer returns hidden revision content in diff
Impact
Read suppressed moderator-redacted post data
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Vulnerability AssessmentAI

Exploitation No authentication, special configuration, or non-default deployment mode is required - CVSS PR:N and AV:N confirm unauthenticated remote exploitation against default Discourse installations that allow public access to post histories. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 3.1 score of 5.3 Medium (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N) accurately captures the network-reachable, zero-complexity, unauthenticated nature of the flaw paired with its limited confidentiality impact scope. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An unauthenticated visitor to a public Discourse forum identifies a post with a visible revision history and requests the revision diffs via the standard API or UI. Because PostRevisionSerializer includes hidden revision content when computing adjacent visible diffs, the response returns the suppressed content - such as a moderator-redacted personal disclosure or removed sensitive detail - without any authentication or privilege required. …
Remediation Upgrade Discourse to one of the patched releases corresponding to your active branch: v2026.6.0, v2026.5.1, v2026.4.2, or v2026.1.5. … Detailed patch versions, workarounds, and compensating controls in full report.
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EUVD-2026-42737 vulnerability details – vuln.today
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