---
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'
---

## Overview

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

- `letta <= 0.16.8`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.