PT-2026-30726 · Unknown · Lichess.Org

Ixsly · Published 2026-04-06 · Updated 2026-04-06 · CVE-2026-35208

Positive Technologies · (AI Summary)

CVSS v4.0

5.3

Medium

AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Name of the Vulnerable Software and Affected Versions lichess.org (affected versions not specified)

Description lichess.org, a free and open-source chess server, had a server-side HTML injection sink in the /streamer endpoint and the homepage “Live streams” widget. Approved streamers could inject arbitrary HTML by including markup in their Twitch or YouTube stream title. While a Content Security Policy (CSP) was in place to block inline script execution, the issue remained exploitable. To trigger this, a Lichess account needed to meet streamer requirements: being older than 2 days with at least 15 games played, or being a verified/titled account, and receiving moderator approval. Once live, Lichess would render the platform title directly into the user interface.

Recommendations At the moment, there is no information about a newer version that contains a fix for this vulnerability.

Improper Encoding or Escaping of Output

XSS

Weakness Enumeration

CWE-116

CWE-79

Related Identifiers

CVE-2026-35208

Affected Products

Lichess.Org

References · 5

• https://nvd.nist.gov/vuln/detail/CVE-2026-35208 · Security Note
• https://github.com/lichess-org/lila/commit/0d5002696ae705e1888bf77de107c73de57bb1b3 · Note
• https://github.com/lichess-org/lila/security/advisories/GHSA-v7gh-939r-pfjq · Note
• https://vimeo.com/1175908262 · Note
• https://twitter.com/CVEnew/status/2041250706951172101 · Twitter Post