Vulnerability · Published Oct 20, 2026 · Assigned by VulnCheck
CVE-2026-77937Letta through 0.16.8 Cross-Tenant Impersonation via user_id Header
High 8.1
In plain English
A high-severity authorization bypass via user-controlled key in letta from letta-ai. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 41% of all known vulnerabilities).
Severity (CVSS 3.1)8.1High
Exploit odds (30 days)0.5%top 58.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known
Official 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.
Affected products (as reported)
Weakness: CWE-639 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
References
- Lasso.security Advisory technical-description, exploit
- https://github.com/letta-ai/letta/blob/1131535716e8a31c9a437f8695e25ac98f203a24/letta/server/rest_api/dependencies.py#L39 technical-description
- VulnCheck Advisory: Letta through 0.16.8 Cross-Tenant Impersonation via user_id Header third-party-advisory