CVE-2021-43840Network attack vector

Authenticated file disclosure via diagnostics asset traversal

Published Dec 17, 2021 · Updated Aug 4, 2024

Path traversal in Discourse MessageBus before 3.3.7 allows remote authenticated users to read server files through the diagnostics route. The diagnostics asset handler extracts the suffix after /assets/ and expands it beneath the asset directory without restricting it to known JavaScript assets. The route must be enabled and accessible, and proxy normalization can limit traversal depth; without a proxy, directory ascent is unbounded.

CVSS severity4.2
Medium
EPSS probability1.87%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Path traversal in Discourse MessageBus before 3.3.7 allows remote authenticated users to read server files through the diagnostics route. The diagnostics asset handler extracts the suffix after /assets/ and expands it beneath the asset directory without restricting it to known JavaScript assets. The route must be enabled and accessible, and proxy normalization can limit traversal depth; without a proxy, directory ascent is unbounded.

The record

CVE
CVE-2021-43840
Published
Dec 17, 2021
Updated
Aug 4, 2024
Vendor
Discourse
Product
MessageBus
Classifications
CWE-22, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 17, 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=< 3.3.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Discourse · MessageBusversion=< 3.3.7

Published CVSS scores

3.5NIST NVDAV:N/AC:M/Au:S/C:P/I:N/A:N
4.2GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:H/I:N/A:N
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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