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CVE-2021-43827

Inline footnotes wrapped in <a> tags can cause errors in discourse-footnotes

4.3 Medium

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
Low
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
Low

Exploit likelihood

0.83%Up 0.2 points since Dec 15, 2021
90%50%10%1%

What each source reports

CVE List Score used 4.3

Inline footnotes wrapped in <a> tags can cause errors in discourse-footnotes

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.

Record
CVE-2021-43827
CVSS 3.1
4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Weakness
CWE-755
Updated
2026-11-02
EUVDEUVD-2021-30707 4.3

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.

Record
EUVD-2021-30707
CVSS 3.1
4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Updated
2026-11-03
NVD 4.3

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.

Record
CVE-2021-43827
CVSS 3.1
4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
CVSS 2.0
4.0 MediumAV:N/AC:L/Au:S/C:N/I:N/A:P
Weakness
CWE-755
Updated
2026-11-02
OSV 4.3

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.

Record
CVE-2021-43827
CVSS 3.1
4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Updated
2026-11-02

Affected products

History

History
RecordedChangedSources
aliasesEUVD
first indexedCVE List, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-43827 is a medium vulnerability (CVSS 4.3) in Discourse Discourse-footnote, published December 14, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.83%, the 57th percentile. No source names a fixed version.

References

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