{"id":"CVE-2026-77937","title":"Letta through 0.16.8 Cross-Tenant Impersonation via user_id Header","summary":"Letta through 0.16.8 contains an authentication bypass vulnerability that allows API callers to impersonate other users by supplying a self-asserted user_id HTTP header. Attackers can set user_id to another tenant's ID, even with LETTA_S…","severity":"high","cvss":8.1,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N","cvssSource":"cna","cwe":["CWE-639"],"vendor":"letta-ai","product":"letta","affected":["letta <= 0.16.8"],"published":"2026-10-20","updated":"2026-10-20","sourceUpdated":"2026-10-20T00:46:14.829Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-77937","references":[{"url":"https://www.lasso.security/vulnerability-database/cve-2026-77937","label":"Lasso.security Advisory"},{"url":"https://github.com/letta-ai/letta/blob/1131535716e8a31c9a437f8695e25ac98f203a24/letta/server/rest_api/dependencies.py#L39"},{"url":"https://www.vulncheck.com/advisories/letta-through-0.16.8-cross-tenant-impersonation-via-user-id-header","label":"VulnCheck Advisory: Letta through 0.16.8 Cross-Tenant Impersonation via user_id Header"}],"tags":["cve.org"],"ingestedAt":"2026-10-20T01:49:42.624Z","slug":"CVE-2026-77937","body":"## Overview\n\nLetta through 0.16.8 contains an authentication bypass vulnerability that allows API callers to impersonate other users by supplying a self-asserted user_id HTTP header. Attackers can set user_id to another tenant's ID, even with LETTA_SERVER_SECURE enabled, to read and modify that user's agents, memory and configuration.\n\n## Affected\n\n- `letta <= 0.16.8`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":45,"depthScoreParts":{"impact":44.6,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}