CVE-2026-45134

## Description The LangSmith SDK's prompt pull methods (`pull_prompt` / `pull_prompt_commit` in Python, `pullPrompt` / `pullPromptCommit` in JS/TS) fetch and deserialize prompt manifests from the LangSmith Hub. These manifests may contain serialized LangChain objects and model configuration that affect runtime behavior. When pulling a public prompt by `owner/name` identifier, the manifest content is controlled by an external party, but prior versions of the SDK did not distinguish this from pulling a prompt within the caller's own organization. Prompt manifests can intentionally configure a model with a custom base URL, default headers, model name, or other constructor arguments. These are supported features, but they also mean the prompt contents should be treated as executable configuration rather than plain text. A prompt can also include serialized LangChain `Runnable` or `PromptTemplate` objects with attacker-controlled constructor kwargs, or secret references that, if `secrets_from_env` is enabled, read environment variables at deserialization time. Applications are exposed when all of the following are true: - The application calls `pull_prompt` or `pull_prompt_commit` (Python) or `pullPrompt` or `pullPromptCommit` (JS/TS) with a public `owner/name` prompt identifier. - The prompt was published or modified by an untrusted or compromised account. - The application uses the pulled prompt without independently validating its contents. Applications that only pull prompts from their own organization (referenced by name only, without an `owner/` prefix) are not affected by the public prompt trust boundary issue described above. However, same-organization prompts carry their own risk. If an attacker gains write access to the organization (for example, through a leaked `LANGSMITH_API_KEY` or a compromised team member account), they can push a malicious prompt that is pulled and deserialized without any additional warning. ## Impact An attacker who publishes a m