What is CVE-2021-43856?

CVE-2021-43856 is a high-severity vulnerability in Requarks Wiki, classified under Cross-site Scripting. CVSS score: 8.2/10. Published 2021-12-27.

How severe is CVE-2021-43856?

High severity. CVSS v3 base score is 8.2 out of 10.

Is CVE-2021-43856 known to be exploited?

2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

XSS in Requarks Wiki

CVE-2021-43856

Wiki.js is a wiki app built on Node.js. Wiki.js 2.5.263 and earlier is vulnerable to stored cross-site scripting through non-image file uploads for file types that can be viewed directly inline in the browser. By creating a malicious file which can execute inline JS when viewed in the browser (e.g. XML files), a malicious Wiki.js user may stage a stored cross-site scripting attack. This allows the attacker to execute malicious JavaScript when the file is viewed directly by other users. The file must be opened directly by the user and will not trigger directly in a normal Wiki.js page. A patch in version 2.5.264 fixes this vulnerability by adding an optional (enabled by default) force download flag to all non-image file types, preventing the file from being viewed inline in the browser. As a workaround, disable file upload for all non-trusted users. --- Thanks to @Haxatron for reporting this vulnerability. Initially reported via https://huntr.dev/bounties/266bff09-00d9-43ca-a4bb-bb540642811f/

Vulnerability class: XSS (Cross-Site Scripting)

Published 2021-12-27 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 8.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N.

EPSS exploit prediction

EPSS: 0.009 (57.7th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 58th percentile — 57.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000

Affected products

Requarks Wiki — versions < 2.5.264
Requarks Wiki.js

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

Public proof-of-concept exploits

References

github.com/Requarks/wiki/security/advisories/GHSA-rhpf-929m-7fm2 (Exploit, Patch, Third Party Advisory)
github.com/Requarks/wiki/commit/79bdd4409316adf649806de3e22352297f85cee0 (Patch, Third Party Advisory)
github.com/Requarks/wiki/releases/tag/2.5.264 (Third Party Advisory, Release Notes)

Frequently asked questions

What is CVE-2021-43856?: CVE-2021-43856 is a high-severity vulnerability in Requarks Wiki, classified under Cross-site Scripting. CVSS score: 8.2/10. Published 2021-12-27.
How severe is CVE-2021-43856?: High severity. CVSS v3 base score is 8.2 out of 10.
Is CVE-2021-43856 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.