Authentication Bypass Vulnerability in Letta by Lasso
CVE-2026-77937

8.6HIGH

Key Information:

Vendor

Letta-ai

Status
Letta
Vendor
CVE Published:
20 October 2026

Badges

👾 Exploit Exists🟡 Public PoC

What is CVE-2026-77937?

The Letta platform, up to version 0.16.8, is susceptible to an authentication bypass vulnerability that enables API callers to impersonate other users. By modifying the 'user_id' HTTP header, attackers can specify the ID of another tenant, allowing unauthorized access to sensitive information related to that user's agents, memory, and configuration. This vulnerability poses a significant concern even when the LETTA_SERVER_SECURE feature is enabled, as it undermines the multi-tenant architecture, potentially compromising user data integrity.

Affected Version(s)

letta 0 <= 0.16.8

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CVE-2026-77937 - Proof of Concept

References

https://www.lasso.security/vulnerability-database/cve-202...
technical-descriptionexploit
https://github.com/letta-ai/letta/blob/1131535716e8a31c9a...
technical-description
https://www.vulncheck.com/advisories/letta-through-0.16.8...
third-party-advisory

CVSS V4

Score:
8.6
Severity:
HIGH
Confidentiality:
High
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

Credit

Noy Pearl
Michael Sromin
Ophir Dror
.