High severity · published Oct 20, 2026
CVE-2026-77937
Letta through 0.16.8 Cross-Tenant Impersonation via user_id Header
8.1
CVSS
0.5%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
High
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.5% · higher than 41% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
LE
letta · letta-ai
through 0.16.8 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-77937
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-77937
github.com
https://github.com/letta-ai/letta/blob/1131535716e8a31c9a437f8695e25ac98f203a24/letta/server/rest_api/dependencies.py#L39
www.lasso.security
https://www.lasso.security/vulnerability-database/cve-2026-77937
www.vulncheck.com
https://www.vulncheck.com/advisories/letta-through-0.16.8-cross-tenant-impersonation-via-user-id-header
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