LangSmith SDK: Public prompt pull deserializes untrusted manifests without trust boundary warning

## 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 malicious prompt to LangSmith Hub may be able to affect applications that pull that prompt by `owner/name`. If the prompt manifest reaches the SDK's deserialization path, the SDK will instantiate the referenced LangChain objects with the attacker-supplied constructor arguments rather than treating the manifest as inert data. Realistic impacts include: - Server-side request forgery (SSRF), outbound request redirection, and interception of LLM traffic if a prompt manifest configures an LLM client with an attacker-controlled `base_url`, proxy, or equivalent endpoint-setting parameter. In typical deployments, redirected requests may include prompt contents, system prompts, retrieved context, model parameters, provider credentials, or other secrets and may disclose them to the attacker-controlled endpoint. - Prompt injection or behavior manipulation if a manifest embeds attacker-controlled system messages, prompt templates, or model parameters that alter the application's behavior. - Additional deserialization risk when `include_model=True` is passed, because this expands the allowlist to partner integration classes. This is not the default, but it materially increases risk when pulling prompts from outside the caller's organization. ## Remediation The LangSmith SDK now blocks pulling public prompts by `owner/name` by default. Callers must explicitly opt in by passing `dangerously_pull_public_prompt=True` (Python) or `dangerouslyPullPublicPrompt: true` (JS/TS) to acknowledge the trust boundary. This flag should only be set after reviewing and trusting the prompt contents, not merely the publishing account. Upgrade to LangSmith SDK **Python >= 0.8.0** or **JS/TS >= 0.6.0**. ### Guidance for prompt pull methods The prompt pull methods (`pull_prompt` / `pull_prompt_commit` in Python, `pullPrompt` / `pullPromptCommit` in JS/TS) should be used only with trusted prompts. Do not pull public prompts by `owner/name` from untrusted or unreviewed sources without understanding

CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:N

Severity from

GitHub (reviewed advisory)

Weakness

CWE-502

Also known as

CVE-2026-45134, PYSEC-2026-2555, PYSEC-2026-2560, PYSEC-2026-2582

• github.com/langchain-ai/langsmith-sdk/security/advisories/GHSA-3644-q5cj-c5c7
• nvd.nist.gov/vuln/detail/CVE-2026-45134
• github.com/langchain-ai/langsmith-sdk