CVE-2026-59152 is a path traversal vulnerability (CWE-22) in the langchain-ai langsmith-sdk's TracingMiddleware component. Prior to version 0.8.18, an attacker who can send HTTP requests to a server running this middleware can cause it to read arbitrary files from the local filesystem and upload their contents to the LangSmith platform as trace attachments. Exploitation may not require authentication depending on deployment. The vulnerability results in a trust-boundary crossing, allowing parties with read access to workspace traces to access files on the server outside the intended scope. The issue is resolved in version 0.8.18.

An attacker with the ability to send HTTP requests to the vulnerable service can cause arbitrary local files to be read and uploaded as trace attachments. This enables unauthorized disclosure of sensitive files from the server's filesystem. The impact is limited by the requirement that the attacker must have read access to the LangSmith workspace traces, but this can include low-privilege workspace members or compromised accounts, thus expanding their access beyond intended boundaries. The vulnerability does not affect confidentiality of the server beyond this trust boundary crossing and does not impact integrity or availability.

Upgrade langsmith-sdk to version 0.8.18 or later, where this vulnerability is fixed. No other mitigation or temporary workaround is indicated. Patch status is not explicitly stated as 'official-fix' in the vendor advisory, but the description confirms the issue is fixed in 0.8.18. There is no indication that the vendor manages this as a cloud service; therefore, manual upgrade is required.