CVE-2026-77937
Letta through 0.16.8 Cross-Tenant Impersonation via user_id Header
letta-ai letta
CVSS
8.6HighExploitationPublic exploit codeCISA's assessment says proof of concept code is public, assessed 20 Oct 2026. Not in the KEV catalogCISA via CVE List
Exploit odds (EPSS)0.40%Chance of exploitation activity in the next 30 days, higher than 33% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed inNone listedNo source names a fixed version. Check the vendor advisory below
What fixes it
No source in this snapshot names a fixed version. The vendor advisories under References are the place to check.
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.
Text from CVE List
Affected versions 1
- lettaaffected: all versions through 0.16.8CVE List
References 3
- vulncheck.com/advisories/letta-through-0.16.8-cross-tenant-impersonation-via-user-id-headerAdvisoryvia CVE List
- lasso.security/vulnerability-database/cve-2026-77937Exploitvia CVE List
- github.com/letta-ai/letta/blob/1131535716e8a31c9a437f8695e25ac98f203a24/letta/server/rest_api/dependencies.py#L39Referencevia CVE List