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Discourse CVE-2026-32244

| EUVDEUVD-2026-30815 MEDIUM
Information Exposure (CWE-200)
2026-05-19 security-advisories@github.com
5.3
CVSS 3.1 · Vendor: github
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Attack ChainAIDerived

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

  1. Access
    Identify Discourse instance with AI summaries enabled
  2. Exploit
    Locate topics where content was recently removed or moderated
  3. Execution
    Request cached AI summary via topic endpoint
  4. Impact
    Receive stale summary exposing removed content

Vulnerability Assessment

Weakness
CWE
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.

Exploitation Conditions

The AI summarization feature must be enabled on the Discourse instance, which requires explicit administrator configuration including a third-party AI API key - this is not enabled in default Discourse installations. A summary must have been generated for a given topic prior to the content removal event. Exploitation is limited to reading summarized text only, not full post content, attachments, or user data. Per the CVSS vector (PR:N/UI:N), no authentication or user interaction is required once those preconditions exist. Exploitation is constrained to instances with AI summarization active and only affects topics for which cached summaries predate a moderation action.

Impact

The CVSS vector (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N) scores this at 5.3 Medium. Attack complexity is low and no authentication is required, meaning any anonymous internet user can attempt to read stale summaries. However, the confidentiality impact is rated Low (C:L), reflecting that only summary text - not raw posts, attachments, or account data - is exposed, and only for topics that had AI summaries generated prior to content removal. EPSS data was not provided; the absence of KEV listing and public POC code suggests this is not actively targeted at scale. Real-world risk is bounded by two factors: the deploying instance must have AI summarization enabled (a non-default, optional feature requiring API key configuration), and exploitation yields only partial, summarized content rather than full post bodies or sensitive metadata. This is a genuine but contained information disclosure - a real priority for communities where removed content may be sensitive (e.g., legal disputes, private forum content), but not an emergency for most deployments without AI features enabled.

Exploit ScenarioDerived

An anonymous user visits a Discourse forum where a topic containing sensitive content (e.g., a private dispute, a post later removed by moderators) had previously had an AI summary generated. After a moderator deletes the offending post, the cached summary remains accessible. The anonymous user fetches the topic's summary endpoint and receives the stale AI-generated text that references or reproduces the removed content. No public exploit code exists, and the attack requires no tooling beyond a standard web browser or HTTP client.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – May 19, 2026

Discourse's AI summarization feature exposes removed or restricted content to anonymous and unprivileged users through stale cached summaries. Affected are all Discourse instances running versions prior to 2026.1.4, 2026.3.1, 2026.4.1, and 2026.5.0-latest.1 with AI summarization enabled. An unauthenticated attacker can read cached summaries that persist after the underlying content has been moderated or deleted, bypassing content removal controls. No public exploit code exists and no KEV listing has been issued at time of analysis.

RemediationAI

Upgrade Discourse to one of the vendor-confirmed fixed releases: stable branch 2026.1.4, beta branch 2026.3.1, tests-passed branch 2026.4.1, or latest branch 2026.5.0-latest.1. Full advisory and upgrade guidance are available at https://github.com/discourse/discourse/security/advisories/GHSA-hjmg-2mww-vfvx. For operators who cannot immediately upgrade, the vendor-documented workaround is to restrict summary generation by tightening the allowed groups on the summarization Personas - limiting which user groups can trigger summary creation prevents fresh summaries from being cached for broad audiences, and reduces the surface area for stale summaries to be exposed. Note that this workaround does not retroactively invalidate existing cached summaries; operators should consider manually purging the AI summary cache after applying group restrictions. Disabling the AI summarization feature entirely eliminates the vulnerability at the cost of losing summarization functionality.

Affected VersionsENISA

discourse < 2026.1.4
discourse 2026.4.0-latest, < 2026.4.1
discourse 2026.3.0-latest, < 2026.3.1
discourse 2026.5.0-latest, < 2026.5.0-latest.1

Affected Packages

euvd discourse fix: 2026.1.4
euvd discourse_2026_3_0_latest fix: 2026.3.1
euvd discourse_2026_4_0_latest fix: 2026.4.1
euvd discourse_2026_5_0_latest fix: 2026.5.0-latest.1

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 4 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 community discussion platform with an integrated AI summarization layer that generates and caches topic or post summaries via configurable 'summarization Personas.' The vulnerability stems from CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor): when content is removed by moderators or administrators, the AI-generated summary cache is not invalidated, leaving a stale representation of the removed content accessible. Because summaries are served to anonymous and low-privilege users who lack the ability to trigger summary regeneration, those users receive a cached view that reflects content the platform has since redacted. The root cause is a cache-coherency failure between the content moderation lifecycle and the AI summary invalidation logic.

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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

Primary rating from Vendor (github) · only source for this CVE.

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

1
Patch available
May 19, 2026 - 01:01 EUVD

DescriptionCVE.org

Discourse is an open-source discussion platform. In versions prior to 2026.1.4, 2026.3.1, 2026.4.1 and 2026.5.0-latest.1, outdated cached AI summaries can leak removed content to anonymous and unprivileged users who cannot regenerate summaries. This issue has been fixed in versions 2026.1.4, 2026.3.1, 2026.4.1 and 2026.5.0-latest.1. To work around this issue, restrict summary generation by tightening the allowed groups on the summarization Personas.

Threat Intelligence Overview

EPSS Score
0.0%
Top 91% exploitable
Data Quality
7 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment 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 0.0%
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

26
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +26
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

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

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