CVE-2026-25528 LangSmith Client SDK Affected by Server-Side Request Forgery via Tracing Header Injection
Attackers can inject malicious URLs via HTTP headers in the LangSmith SDK, causing sensitive trace data to be sent to attacker-controlled endpoints.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-25528?
CVE-2026-25528 is a medium-severity server-side request forgery vulnerability in langchain-ai langsmith-sdk, published on 9 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-918
Which versions are affected by CVE-2026-25528?
5 open source packages ship an affected version, including langsmith.
| Package | Affected | Fixed in |
|---|---|---|
langsmith PyPI | From 0.4.10 | 0.6.3 |
langsmith PyPI | From 0.4.10 | 0.6.3 |
langsmith PyPI | From 0.4.10 | 0.6.3 |
langsmith npm | From 0.3.41 | 0.4.6 |
langsmith npm | From 0.3.41 | 0.4.6 |
How do I fix CVE-2026-25528?
Upgrade langsmith to a fixed version for your release line: 0.6.3 or 0.4.6.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-25528 being exploited?
There is no known exploitation of CVE-2026-25528 in the wild and no public exploit code.
Sources
Also known as ECHO-f9e2-5c88-6463, GHSA-v34v-rq6j-cj6p, MINI-6xxj-g8px-5m8q, MINI-757g-82c7-r5h3, MINI-jpc4-q8gv-fw23, MINI-qm5h-jf8w-288v and 2 more.