XSS in Lichess-Org Lila
CVE-2026-103974
lichess.org is the forever free, adless and open source chess server. Prior to commit c54596c9e1569d378fe20f80d4c790c6fdee54c4, a user who can add a chapter to a study can place attacker-controlled text in the PGN Annotator tag, which becomes Comment.Author.External and is returned verbatim by authorText. When a study node has at least two comments, ui/analyse/src/treeView/inlineView.ts interpolates that author string into HTML passed to the innerHTML hook without escaping it. Opening the affected study can therefore render stored attacker-controlled HTML and CSS for other viewers, including navigation to an attacker-controlled site, content spoofing, and CSS-based data exposure, although the site's content security policy blocks injected JavaScript. This vulnerability is fixed by commit c54596c9e1569d378fe20f80d4c790c6fdee54c4.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
- Lichess-Org Lila — versions < c54596c9e1569d378fe20f80d4c790c6fdee54c4
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-103974?
- CVE-2026-103974 is a medium-severity vulnerability in Lichess-Org Lila, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2026-10-14.
- How severe is CVE-2026-103974?
- Medium severity. CVSS v3 base score is 5.4 out of 10.