XSS in Outline

CVE-2026-43887

Outline is a service that allows for collaborative documentation. From 0.84.0 to 1.6.1, the Outline comment section permits users to mention other users; however, the backend does not validate or sanitize the href attribute associated with these mentions. As a result, potentially dangerous protocols (e.g., javascript:) are not filtered, introducing a risk of client-side code execution. This vulnerability is fixed in 1.7.0.

Vulnerability class: XSS (Cross-Site Scripting)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 7.3 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N.

EPSS exploit prediction

EPSS: 0.004 (35.3th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 35th percentile — 35.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-43887: held from 0.002 to 0.004.

EPSS over last 30 days · oldest: 0.002 · newest: 0.004 · change: +0.002

Affected products

  • Outline — versions >= 0.84.0, < 1.7.0

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-43887?
CVE-2026-43887 is a high-severity vulnerability in Outline, classified under Cross-site Scripting. CVSS score: 7.3/10. Published 2026-05-11.
How severe is CVE-2026-43887?
High severity. CVSS v3 base score is 7.3 out of 10.