CVE-2026-77937

CVSS 8.6 (high) · published 2026-10-20

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_SERVER_SECURE enabled, to read and modify that user's agents, memory and configuration.

Weakness: CWE-639

Source: NVD CVE-2026-77937

References

• https://github.com/letta-ai/letta/blob/1131535716e8a31c9a437f8695e25ac98f203a24/letta/server/rest_api/dependencies.py#L39
• https://www.lasso.security/vulnerability-database/cve-2026-77937
• https://www.vulncheck.com/advisories/letta-through-0.16.8-cross-tenant-impersonation-via-user-id-header

Check your software

Connect an AI agent to the FixLane MCP server or ask the Telegram bot to check what you have installed against incidents with a verified fixed version.