What’s Vulnerable › Vulnerabilities

CVE-2026-103974: lichess.org: Stored HTML Injection via PGN Annotator Tag in Studies

• Severity: medium (CVSS 5.4 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: 2026-10-14 · updated 2026-10-16
• Weakness: CWE-79

Description

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.

Affected products

• lichess-org lila: before c54596c9e1569d378fe20f80d4c790c6fdee54c4

References

• https://github.com/lichess-org/lila/commit/c54596c9e1569d378fe20f80d4c790c6fdee54c4
• https://github.com/lichess-org/lila/security/advisories/GHSA-43g7-r6hp-ccf8
• https://github.com/lichess-org/lila/security/advisories/GHSA-43g7-r6hp-ccf8

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