CVE-2026-77937
Letta through 0.16.8 Cross-Tenant Impersonation via user_id Header
CVSS Score
8.1
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-639 |
| Vendor | letta-ai |
| Product | letta |
| Published | Oct 20, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None
Affected Versions
letta-ai / letta
0 ≤ 0.16.8
References
lasso.security: https://www.lasso.security/vulnerability-database/cve-2026-77937 github.com: https://github.com/letta-ai/letta/blob/1131535716e8a31c9a437f8695e25ac98f203a24/letta/server/rest_api/dependencies.py#L39 vulncheck.com: https://www.vulncheck.com/advisories/letta-through-0.16.8-cross-tenant-impersonation-via-user-id-header
Credits
Noy Pearl Michael Sromin Ophir Dror