What is the CVSS score of CVE-2026-59828?

CVE-2026-59828 has a CVSS 3.1 base score of 5.3 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N. EPSS exploitation probability: 0.3%.

Is there a patch available for CVE-2026-59828?

Yes, a patch is available for CVE-2026-59828. Update the affected software to the latest version immediately.

Discourse CVE-2026-59828

EUVD-2026-42737 MEDIUM

Information Exposure (CWE-200)

2026-07-09 security-advisories@github.com

Information Disclosure Discourse

5.3

CVSS 3.1 · Vendor: github

View

Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

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

Vulnerability Assessment

Weakness	CWE CWE-200 OWASP Top 10:2025 A01:2025 - Broken Access Control ASVS 5.0 V14 - Data Protection Data exposure prevention MITRE ATT&CK 2 techniques across 2 tactics: Collection, Discovery The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Exploitation Conditions	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. The one practical limiting factor is that a target post must have at least one hidden revision adjacent to one or more visible revisions; if no hidden revisions exist on a post, there is no suppressed content to leak. Exploitation is constrained to reading hidden revision content only - there is no code execution, data modification, or availability impact. Instances where revision history is restricted to logged-in users only would reduce the exposed audience but would not eliminate the flaw for authenticated-but-unprivileged users.
Impact	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. The 'Low' confidentiality rating reflects partial information disclosure, but real-world severity scales with what hidden revisions actually contain - if moderators routinely redact PII, private user disclosures, or abuse reports, the practical data exposure risk is higher than the Medium score suggests. No EPSS score was provided in the available data, making quantitative exploitation probability unavailable. The absence of a CISA KEV listing and no known public POC reduces urgency somewhat, though the trivial exploit path (unauthenticated, no special config) means the barrier to abuse is extremely low should the mechanism become public knowledge. For community-facing Discourse instances where public revision browsing is enabled, this warrants prompt patching rather than deferral.
Exploit ScenarioDerived	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. No public POC is known at time of analysis, but the mechanism is straightforward and derivable from the patch commits.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).

Patch available 0.3% exploitation probability (EPSS)

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AnalysisAIv1 – Jul 09, 2026

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. No active exploitation has been identified at time of analysis, but the unauthenticated, low-complexity attack vector means any visitor to a vulnerable Discourse instance can potentially access suppressed post content - including moderator-redacted material - without any credentials or special access.

RemediationAI

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. Fix commits are available at the Discourse GitHub repository (commits 1f26c116, 8b773332, 8d36da1b, d58988d4) and the full security advisory is at https://github.com/discourse/discourse/security/advisories/GHSA-q456-4f8q-42vx. If an immediate upgrade is not feasible, a compensating control is to restrict access to the post revision history API endpoints (typically /posts/:id/revisions/) via web server rules or a WAF, accepting the trade-off that all users - including legitimate ones - will lose access to revision diffs until the upgrade is applied. No vendor-documented workarounds beyond patching are identified in available data.

Affected VersionsENISA

discourse 2026.5.0-latest, < 2026.5.1

discourse 2026.1.0-latest, < 2026.1.5

discourse 2026.4.0-latest, < 2026.4.2

Affected Packages

euvd discourse_2026_1_0_latest fix: 2026.1.5

euvd discourse_2026_4_0_latest fix: 2026.4.2

euvd discourse_2026_5_0_latest fix: 2026.5.1

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 3 packages in euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

Discourse is an open-source Ruby on Rails-based discussion platform. The vulnerability resides in PostRevisionSerializer, the component responsible for serializing post edit history and generating revision diffs for client consumption. Post revisions can be individually hidden from regular users - a common moderation action to remove sensitive disclosures, PII, or inappropriate content from public view. The serializer failed to apply these visibility access controls consistently when computing diffs between adjacent revisions, causing hidden revision content to bleed into the serialized output for neighboring visible revisions. CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor) precisely characterizes the root cause: an access control enforcement gap at the serialization layer, not at the data storage or retrieval layer. No CPE strings were provided in the available data; affected scope is identified from the GitHub release history across multiple maintained branches.

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Exploit and PoC references, threat intelligence from 22 sources

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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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

None

Lifecycle Timeline

Patch available

Jul 09, 2026 - 23:02 EUVD

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.

Threat Intelligence Overview

EPSS Score

0.3%

Top 77% exploitable

Prevalence

Medium

popular open-source forum platform, widely self-hosted across communities

Social Media

Sightings

Data Quality

6 sources

Confidence: High

EUVD

NVD

CVE.org

EPSS

Vulnrichment CIRCL

GitHub

VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity MEDIUM

CISA KEV No

Public POC No

EPSS 0.3%

Patch available Yes

Active threat No

Deciding rule

MEDIUM severity (CVSS 4.0-6.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Scheduled

Exploitation

None

System Exposure· derived

Open

Automatable

Yes

Human Impact· derived

Medium

Technical Impact

Partial

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +26

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.