Chainlit contains a session hijacking vulnerability

Chainlit before 2.10.1 contains a session hijacking vulnerability that allows unauthenticated attackers to restore and inherit authenticated user sessions by presenting a valid sessionId during WebSocket session restoration without ownership verification. Attackers can exploit the restore_existing_session path to assume a victim's permissions and roles, enabling unauthorized invocation of tools and access to data restricted to the authenticated victim.

CVSS 3.1

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Severity from

GitHub (reviewed advisory)

Weakness

CWE-862

Also known as

CVE-2026-56104

• nvd.nist.gov/vuln/detail/CVE-2026-56104
• github.com/Chainlit/chainlit/pull/2857
• github.com/Chainlit/chainlit/commit/5effb664f1e0af4a4f0a42fe63ea979676039a7f
• github.com/Chainlit/chainlit
• github.com/Chainlit/chainlit/releases/tag/2.10.1
• www.vulncheck.com/advisories/chainlit-session-hijacking-via-websocket-session-restoration