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.

Attack Vector Network

Attack Complexity Low

Privileges Required Low

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact High

Vulnerable System Integrity Impact High

Vulnerable System Availability Impact None

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00401.

Exploitation poc

Automatable no

Technical Impact total

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
letta-ai letta unaffected
Version Status Constraints
0 affected ≤ 0.16.8

No data.

No data.

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Project Subscriptions

Vendors Products
Letta Subscribe
Letta Subscribe
Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

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

Tue, 20 Oct 2026 14:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Tue, 20 Oct 2026 01:15:00 +0000

Type Values Removed Values Added
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.
Title Letta through 0.16.8 Cross-Tenant Impersonation via user_id Header
First Time appeared Letta
Letta letta
Weaknesses CWE-639
CPEs cpe:2.3:a:letta:letta:*:*:*:*:*:*:*:*
Vendors & Products Letta
Letta letta
References
Metrics cvssV3_1

{'score': 8.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N'}

cvssV4_0

{'score': 8.6, 'vector': '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'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-10-20T13:48:37.840Z

Reserved: 2026-08-21T17:52:36.080Z

Link: CVE-2026-77937

cve-icon Vulnrichment

Updated: 2026-10-20T13:48:32.739Z

cve-icon NVD

Status : Received

Published: 2026-10-20T01:17:20.263

Modified: 2026-10-20T14:17:01.193

Link: CVE-2026-77937

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-20T12:30:06Z

Weaknesses