CVE-2021-37703Network attack vector

Read-state disclosure via overbroad MessageBus publication

Published Aug 13, 2021 · Updated Aug 4, 2024

Information exposure in Discourse before 2.7.8 and 2.8.0.beta5 allows remote attackers to read a user's topic read state. TopicTrackingState.publish_unread routes per-user payloads through MessageBus too broadly, exposing last-read post numbers and notification levels to unauthorized clients. Exploitation requires user interaction and exposes read-state metadata without reported modification or service interruption.

CVSS severity4.3
Medium
EPSS probability0.84%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information exposure in Discourse before 2.7.8 and 2.8.0.beta5 allows remote attackers to read a user's topic read state. TopicTrackingState.publish_unread routes per-user payloads through MessageBus too broadly, exposing last-read post numbers and notification levels to unauthorized clients. Exploitation requires user interaction and exposes read-state metadata without reported modification or service interruption.

The record

CVE
CVE-2021-37703
Published
Aug 13, 2021
Updated
Aug 4, 2024
Vendor
Discourse
Product
Discourse
Classifications
CWE-200, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 13, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record 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=< 2.7.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Discourse · Discourseversion=< 2.7.8

Published CVSS scores

4.3GitHub CNACVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
4.3NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A: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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-200Exposure of Sensitive Information to an Unauthorized Actor
T1190Exploit Public-Facing Application

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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