CVE-2026-35208

Summary

lichess.org is the forever free, adless and open source chess server. Any approved streamer can inject arbitrary HTML into /streamer and the homepage “Live streams” widget by placing markup in their Twitch/YouTube stream title. CSP is present and blocks inline script execution, but the issue is still a server-side HTML injection sink. To trigger this, a Lichess account only needs to satisfy the normal streamer requirements and get approved. Per Streamer.canApply, that means an account older than 2 days with at least 15 games, or a verified/titled account. After moderator approval, once the streamer goes live, Lichess pulls the platform title and renders it into the UI as-is. No extra privileges are needed beyond a normal approved streamer profile. This vulnerability is fixed with commit 0d5002696ae705e1888bf77de107c73de57bb1b3.

Affected Software

VendorProductVersion RangeStatus
lichess-orglila< 0d5002696ae705e1888bf77de107c73de57bb1b3affected

Weaknesses

  • CWE-79: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
  • CWE-116: CWE-116: Improper Encoding or Escaping of Output

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

References