CVE-2026-35208

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.

CVSS v3 5.4 MEDIUM

5.4^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.3 / Impact : 2.7

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required LOW

User Interaction REQUIRED

Confidentiality Impact LOW

Integrity Impact LOW

Availability Impact NONE

Scope CHANGED

References

Link	Resource
https://github.com/lichess-org/lila/commit/0d5002696ae705e1888bf77de107c73de57bb1b3	Patch
https://github.com/lichess-org/lila/security/advisories/GHSA-v7gh-939r-pfjq	Exploit Vendor Advisory
https://vimeo.com/1175908262	Exploit

Configurations

Configuration 1 (hide)

cpe:2.3:a:lichess:lila:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-04-06 21:16

Updated : 2026-07-24 21:10

NVD link : CVE-2026-35208

Mitre link : CVE-2026-35208

CVE.ORG link : CVE-2026-35208

JSON object : View

Products Affected

lichess

lila

CWE

CWE-79

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CWE-116

Improper Encoding or Escaping of Output

{"id": "CVE-2026-35208", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-35208", "role": "CISA Coordinator", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "version": "2.0.3", "timestamp": "2026-04-07T14:55:58.549189Z"}}], "cvssMetricV31": [{"type": "Primary", "source": "nvd@nist.gov", "cvssData": {"scope": "CHANGED", "version": "3.1", "baseScore": 5.4, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N", "integrityImpact": "LOW", "userInteraction": "REQUIRED", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "LOW", "confidentialityImpact": "LOW"}, "impactScore": 2.7, "exploitabilityScore": 2.3}], "cvssMetricV40": [{"type": "Secondary", "source": "security-advisories@github.com", "cvssData": {"Safety": "NOT_DEFINED", "version": "4.0", "Recovery": "NOT_DEFINED", "baseScore": 5.3, "Automatable": "NOT_DEFINED", "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/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", "exploitMaturity": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED", "userInteraction": "NONE", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "LOW", "subIntegrityImpact": "NONE", "vulnIntegrityImpact": "LOW", "integrityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "availabilityRequirement": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "subConfidentialityImpact": "NONE", "vulnConfidentialityImpact": "LOW", "confidentialityRequirement": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED"}}]}, "affected": [{"source": "security-advisories@github.com", "affectedData": [{"vendor": "lichess-org", "product": "lila", "versions": [{"status": "affected", "version": "< 0d5002696ae705e1888bf77de107c73de57bb1b3"}]}]}], "published": "2026-04-06T21:16:20.273", "references": [{"url": "https://github.com/lichess-org/lila/commit/0d5002696ae705e1888bf77de107c73de57bb1b3", "tags": ["Patch"], "source": "security-advisories@github.com"}, {"url": "https://github.com/lichess-org/lila/security/advisories/GHSA-v7gh-939r-pfjq", "tags": ["Exploit", "Vendor Advisory"], "source": "security-advisories@github.com"}, {"url": "https://vimeo.com/1175908262", "tags": ["Exploit"], "source": "security-advisories@github.com"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Secondary", "source": "security-advisories@github.com", "description": [{"lang": "en", "value": "CWE-79"}, {"lang": "en", "value": "CWE-116"}]}], "descriptions": [{"lang": "en", "value": "lichess.org is the forever free, adless and open source chess server. Any approved streamer can inject arbitrary HTML into /streamer and the homepage \u201cLive streams\u201d 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."}, {"lang": "es", "value": "lichess.org es el servidor de ajedrez para siempre gratuito, sin anuncios y de c\u00f3digo abierto. Cualquier streamer aprobado puede inyectar HTML arbitrario en /streamer y el widget 'Live streams' de la p\u00e1gina de inicio colocando marcado en el t\u00edtulo de su transmisi\u00f3n de Twitch/YouTube. CSP est\u00e1 presente y bloquea la ejecuci\u00f3n de scripts en l\u00ednea, pero el problema sigue siendo un sumidero de inyecci\u00f3n de HTML del lado del servidor. Para activar esto, una cuenta de Lichess solo necesita satisfacer los requisitos normales de streamer y ser aprobada. Seg\u00fan Streamer.canApply, eso significa una cuenta con m\u00e1s de 2 d\u00edas de antig\u00fcedad con al menos 15 partidas, o una cuenta verificada/con t\u00edtulo. Despu\u00e9s de la aprobaci\u00f3n del moderador, una vez que el streamer se conecta en vivo, Lichess extrae el t\u00edtulo de la plataforma y lo renderiza en la interfaz de usuario tal cual. No se necesitan privilegios adicionales m\u00e1s all\u00e1 de un perfil de streamer aprobado normal. Esta vulnerabilidad se corrige con el commit 0d5002696ae705e1888bf77de107c73de57bb1b3."}], "lastModified": "2026-07-24T21:10:00.143", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:lichess:lila:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "A9D5C218-3446-4056-881F-89DBF44EA3C9", "versionEndExcluding": "2026-03-31"}], "operator": "OR"}]}], "sourceIdentifier": "security-advisories@github.com"}