CVE-2021-43827
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.
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
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 Medium
CVSS: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 Medium
CVSS: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 Medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L - CVSS 2.0
- 4.0 Medium
AV: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 Medium
CVSS: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
| Recorded | Changed | Sources |
|---|---|---|
| aliases | EUVD | |
| first indexed | CVE 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.