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TI-2026-76667 Aliases CVE-2026-77937

Letta lets API callers impersonate other users via user_id header

Priority HIGH 72CWE-639Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
Security bypass
Confidentiality · integrity · availability
High · High · None
Fix status
No fix listed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-639.

Summary

Letta through 0.16.8 trusts a self-asserted user_id HTTP header, an authorization bypass through a key the user controls (CWE-639). An API caller with low privileges can set user_id to another tenant's ID, even with LETTA_SERVER_SECURE enabled, and read or modify that user's agents, memory and configuration. A proof-of-concept exploit is linked in the references.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

Description from the CNA

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00473 41st percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by the CNA
Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
letta-ailettaup to 0.16.8—No fix listedCNA
  • letta Vendorletta-ai Affected up to 0.16.8 Fixed in — No fix listed CNA

Remediation

The sources list no fixed version for letta.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

Timeline

  1. 2026-10-20 Threatist record created from CVE-2026-77937
  2. 2026-10-20 CISA SSVC decision points changed
  3. 2026-10-20 Priority changed: MEDIUM → HIGH

References

Exploit 1

Other 1

  • TI-2026-76666 Insecure default configuration in Letta exposes API and PostgreSQL CVSS 4.0CRITICAL 9.3
  • TI-2026-15517 letta-ai LettaBot API Status Route server.ts missing authentication CVSS 4.0MEDIUM 6.9
  • TI-2026-76668 Letta tool sandbox exposes server secrets to tool users CVSS 4.0HIGH 7.1
  • TI-2025-05511 letta-ai letta interface.py function_message eval injection CVSS 4.0MEDIUM 5.1

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences