CVE-2026-59152 is a path traversal vulnerability in the langchain-ai langsmith-sdk prior to version 0.8.18. The flaw allows an attacker who can send HTTP requests to a server running the TracingMiddleware component to read arbitrary files from the server's local filesystem. These files are then uploaded as trace attachments to the LangSmith platform. Exploitation may not require authentication depending on deployment. The vulnerability results in a trust boundary crossing, enabling parties with workspace trace-read access to access files beyond their authorized scope. The issue is resolved in version 0.8.18.

An attacker with the ability to send HTTP requests to a vulnerable server can cause it to disclose arbitrary local files by uploading their contents as trace attachments. This allows users with read access to LangSmith workspace traces to access sensitive files on the server, violating intended trust boundaries. The impact is limited to confidentiality (partial information disclosure) and requires at least low privilege (workspace trace-read access). There is no impact on integrity or availability.

Upgrade langsmith-sdk to version 0.8.18 or later, where this path traversal vulnerability is fixed. No other mitigations are indicated. Patch status is not explicitly stated as 'official-fix' but the description confirms the issue is fixed in 0.8.18. There is no indication that this is a cloud service; therefore, user-side patching is required.