CVE-2026-77937
Letta through 0.16.8 Cross-Tenant Impersonation via user_id Header
- State
- Published
- Severity
- 8.6 High
- Published
- Oct 20, 2026
- Updated
- Oct 20, 2026
- Reserved
- Aug 21, 2026
Description
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 8.6 High | CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N | VulnCheck |
| 3.1 | 8.1 High | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N | VulnCheck |
Weaknesses
- CWE-639 Authorization Bypass Through User-Controlled Key
Affected Products
| Product | Versions |
|---|---|
lettaletta-ai |
|
References
- Lasso.security Advisorytechnical-descriptionexploit
- https://github.com/letta-ai/letta/blob/1131535716e8a31c9a437f8695e25ac98f203a24/letta/server/rest_api/dependencies.py#L39technical-description
- VulnCheck Advisory: Letta through 0.16.8 Cross-Tenant Impersonation via user_id Headerthird-party-advisory
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