CVE-2026-43887

High

Published: 11 May 2026

Published

11 May 2026

Modified

15 May 2026

KEV Added

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Patch

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CVSS Score v3.1 7.3 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N

EPSS Score 0.0004 11.5th percentile

Risk Priority 15 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-43887 is a high-severity Cross-site Scripting (CWE-79) vulnerability. Its CVSS base score is 7.3 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 11.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

EU & UK References

🇪🇺 ENISA EUVD: EUVD-2026-29331

Vulnerability details

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.

CWE(s): CWE-79

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

T1059.007 JavaScript Execution

Adversaries may abuse various implementations of JavaScript for execution.

attack.mitre.org →

Why these techniques?

XSS (CWE-79) in web app comment/mention feature allows unsanitized javascript: href injection, directly enabling client-side JS execution via exploitation of the application.

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1