What is the CVSS score of CVE-2021-43827?

CVE-2021-43827 has a CVSS 3.1 base score of 4.3 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L. EPSS exploitation probability: 0.8%.

Is there a patch available for CVE-2021-43827?

Yes, a patch is available for CVE-2021-43827. Update the affected software to the latest version immediately.

Discourse CVE-2021-43827

MEDIUM

Improper Handling of Exceptional Conditions (CWE-755)

2021-12-14 security-advisories@github.com

Information Disclosure Discourse Discourse Footnote

4.3

CVSS 3.1 · Vendor: github

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Vulnerability Assessment

Weakness	CWE CWE-755 OWASP Top 10:2025 A10:2025 - Mishandling of Exceptional Conditions ASVS 5.0 V16 - Security Logging and Error Handling Exception handling procedures
Impact	CVSS score of 4.3 (MEDIUM). Attack characteristics: network attack vector, low complexity, low privileges required, no user interaction not required.
Exploit ScenarioDerived	This vulnerability can be exploited remotely over the network. Successful exploitation could compromise the medium-severity affected system.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).

Patch available 0.8% exploitation probability (EPSS)

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AnalysisAI

discourse-footnote is a library providing footnotes for posts in Discourse. Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable, low attack complexity.

RemediationAI

A vendor patch is available. Apply the latest security update as soon as possible. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

This vulnerability is classified under CWE-755. discourse-footnote is a library providing footnotes for posts in Discourse.

Impact When posting an inline footnote wrapped in `<a>` tags (e.g. `<a>^[footnote]</a>`, the resulting rendered HTML would include a nested `<a>`, which is stripped by Nokogiri because it is not valid. This then caused a javascript error on topic pages because we were looking for an `<a>` element inside the footnote reference span and getting its ID, and because it did not exist we got a null reference error in javascript. Users are advised to update to version 0.2. As a workaround editing offending posts from the rails console or the database console for self-hosters, or disabling the plugin in the admin panel can mitigate this issue. Affected products include: Discourse Discourse Footnote. Version information: version 0.2..

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (github) PRIMARY 4.3 MEDIUM

AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

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

CVSS VectorVendor: github

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

Low

DescriptionCVE.org

discourse-footnote is a library providing footnotes for posts in Discourse.

Impact When posting an inline footnote wrapped in `<a>` tags (e.g. `<a>^[footnote]</a>`, the resulting rendered HTML would include a nested `<a>`, which is stripped by Nokogiri because it is not valid. This then caused a javascript error on topic pages because we were looking for an `<a>` element inside the footnote reference span and getting its ID, and because it did not exist we got a null reference error in javascript. Users are advised to update to version 0.2. As a workaround editing offending posts from the rails console or the database console for self-hosters, or disabling the plugin in the admin panel can mitigate this issue.

Threat Intelligence Overview

EPSS Score

0.8%

Top 48% exploitable

Data Quality

3 sources

Confidence: Low

NVD

CVE.org

EPSS

GitHub

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 0.8%

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· derived

None

System Exposure· derived

Open

Automatable· derived

Human Impact· derived

Medium

Priority Score

Low Medium High Critical

KEV: 0

EPSS: +1

CVSS: +22

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

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