CVE-2026-31869Network attack vector

Authenticated hidden-group membership disclosure via mentions oracle

Published Mar 20, 2026 · Updated Mar 20, 2026

Improper authorization in affected Discourse 2026.1, 2026.2, and 2026.3 releases allows remote authenticated users to infer hidden group membership. ComposerController#mentions accepts allowed_names for a hidden-membership group and returns a private user_reasons value when each probed username belongs to that group. The oracle is reachable only when the authenticated user can message the hidden group, and it discloses membership without exposing message content or granting group access.

CVSS severity5.3
Medium
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authorization in affected Discourse 2026.1, 2026.2, and 2026.3 releases allows remote authenticated users to infer hidden group membership. ComposerController#mentions accepts allowed_names for a hidden-membership group and returns a private user_reasons value when each probed username belongs to that group. The oracle is reachable only when the authenticated user can message the hidden group, and it discloses membership without exposing message content or granting group access.

The record

CVE
CVE-2026-31869
Published
Mar 20, 2026
Updated
Mar 20, 2026
Vendor
Discourse
Product
Discourse
Classifications
CWE-862, CWE-639, CWE-285, CWE-200, T1069
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 2026.1.0-latest, < 2026.1.2
  2. Affected versionversion=>= 2026.2.0-latest, < 2026.2.1
  3. Affected versionversion== 2026.3.0-latest

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Discourse · Discourseversion=>= 2026.1.0-latest, < 2026.1.2; version=>= 2026.2.0-latest, < 2026.2.1; version== 2026.3.0-latest

Published CVSS scores

4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
5.3GitHubCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-862Missing Authorization
CWE-639Authorization Bypass Through User-Controlled Key
CWE-285Improper Authorization
CWE-200Exposure of Sensitive Information to an Unauthorized Actor
T1069Permission Groups Discovery

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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