CVE-2026-43887: Outline: Stored XSS via Comment Mentions

Severity: high (CVSS 7.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-11 · updated 2026-06-17
Weakness: CWE-79

Description

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.

Affected products

outline: from 0.84.0, < 1.7.0

References

https://github.com/outline/outline/security/advisories/GHSA-rqrg-f3qc-xvgh
https://github.com/outline/outline/security/advisories/GHSA-rqrg-f3qc-xvgh

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