---
id: CVE-2026-103974
title: 'lichess.org is the forever free, adless and open source chess server'
summary: >-
  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
  be…
severity: medium
cvss: 5.4
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N'
cwe:
  - CWE-79
published: '2026-10-14'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T20:17:29.167'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-103974'
references:
  - url: >-
      https://github.com/lichess-org/lila/commit/c54596c9e1569d378fe20f80d4c790c6fdee54c4
    label: security-advisories@github.com
  - url: >-
      https://github.com/lichess-org/lila/security/advisories/GHSA-43g7-r6hp-ccf8
    label: security-advisories@github.com
  - url: >-
      https://github.com/lichess-org/lila/security/advisories/GHSA-43g7-r6hp-ccf8
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
  - cve.org
  - exploit-available
ingestedAt: '2026-10-14T19:49:57.605Z'
vendor: lichess-org
product: lila
affected:
  - lila < c54596c9e1569d378fe20f80d4c790c6fdee54c4
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-10-14T19:40:54.734332Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.