CVE-2026-25528: LangSmith Client SDK Server-Side Request Forgery via Tracing Header Injection
Summary
CVE-2026-25528: LangSmith Client SDK Affected by Server-Side Request Forgery via Tracing Header Injection. Affects langsmith versions >= 0.4.10, < 0.6.3. Fixed in 0.6.3. How to fix ↓
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Background
LangSmith is a software development kit (SDK) designed for integrating distributed tracing capabilities into applications. It allows developers to monitor and analyze the performance of their applications by capturing trace data. However, the SDK has a vulnerability that can be exploited through malicious HTTP headers, specifically the baggage header, which can lead to unauthorized data exfiltration.
Vulnerability Detail
The LangSmith SDK's distributed tracing feature is susceptible to Server-Side Request Forgery (SSRF) due to the lack of validation on incoming HTTP headers. Attackers can inject arbitrary api_url values into the baggage header, causing the SDK to send sensitive trace data to attacker-controlled endpoints. This vulnerability arises from the SDK's methods, RunTree.from_headers() in Python and RunTree.fromHeaders() in Typescript, which accept untrusted input without proper filtering. The consequences include data exfiltration of sensitive information such as LLM prompts and application metadata, as well as the potential for the server to make requests to internal services.
How To Fix
Latest published version: 0.14.12 as of 22 Oct 2026
pip install --upgrade "langsmith==0.14.12"Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
0.6.3
This is the first release that contains the fix.
pip install --upgrade "langsmith==0.6.3"Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
If immediate upgrading is not possible, consider implementing the following workaround: Strip or validate the baggage header before passing it to the from_headers() method. For example, you can use the following code snippet in Python:
def validate_baggage_header(baggage_header):
# Implement validation logic to strip unsafe fields
safe_baggage = {} # Initialize a safe baggage dictionary
# Add logic to filter out unsafe fields
return safe_baggage
Conclusion
The LangSmith Client SDK is vulnerable to Server-Side Request Forgery due to improper handling of HTTP headers. It is crucial to update to the latest patched versions to mitigate this risk. If an immediate update is not feasible, implementing header validation can serve as a temporary workaround.
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FAQ
CVE-2026-25528 is a vulnerability in the LangSmith Client SDK that allows for Server-Side Request Forgery through the injection of malicious HTTP headers.
An attacker can exploit this vulnerability by sending a crafted HTTP request with a malicious baggage header, causing the SDK to send sensitive data to an attacker-controlled endpoint.
Sensitive trace data, including LLM prompts, completions, and application metadata, are at risk of being exfiltrated to unauthorized servers.
If you cannot upgrade, you should validate or strip the baggage header before processing it to prevent the injection of unsafe fields.
You can use Vulert, which monitors and alerts in real-time for open-source vulnerabilities in your software. You can also check your application for vulnerabilities using the Vulert playground without any signup.
References
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