CVE-2021-43827Network attack vector

Topic-page disruption via missing footnote link

Published Dec 14, 2021 · Updated Aug 4, 2024

Improper missing-value handling in Discourse Footnote before 0.2 allows remote authenticated users to disrupt topic-page rendering. Anchor-wrapped inline footnotes produce nested links that Nokogiri removes, while the client script dereferences the missing link without a null check. Posting crafted footnote markup is required, and affected readers encounter a JavaScript error rather than data disclosure or modification.

CVSS severity4.3
Medium
EPSS probability0.80%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper missing-value handling in Discourse Footnote before 0.2 allows remote authenticated users to disrupt topic-page rendering. Anchor-wrapped inline footnotes produce nested links that Nokogiri removes, while the client script dereferences the missing link without a null check. Posting crafted footnote markup is required, and affected readers encounter a JavaScript error rather than data disclosure or modification.

The record

CVE
CVE-2021-43827
Published
Dec 14, 2021
Updated
Aug 4, 2024
Vendor
Discourse
Product
Discourse Footnote
Classifications
CWE-230, CWE-755, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 14, 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=< 0.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Discourse · Discourse Footnoteversion=< 0.2

Published CVSS scores

4.0NIST NVDAV:N/AC:L/Au:S/C:N/I:N/A:P
4.3GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-230Improper Handling of Missing Values
CWE-755Improper Handling of Exceptional Conditions
T1499.004Application or System Exploitation

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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