DEV Community

CVE Reports
CVE Reports

Posted on • Originally published at cvereports.com

CVE-2026-27795: The Chain Breaker: Bypassing LangChain's SSRF Guards

#security #cve #cybersecurity

The Chain Breaker: Bypassing LangChain's SSRF Guards

Vulnerability ID: CVE-2026-27795
CVSS Score: 4.1
Published: 2026-02-25

A sophisticated Server-Side Request Forgery (SSRF) bypass was discovered in the @langchain/community package, specifically within the RecursiveUrlLoader. Despite previous attempts to secure this component against internal network scanning, the implementation failed to handle HTTP redirects manually. This allowed attackers to supply a benign, validated URL that subsequently redirected the server's HTTP client to sensitive internal resources (like AWS Metadata services or local admin panels), completely bypassing the initial security checks. This vulnerability highlights the classic 'Check-Then-Act' race condition in web security.

TL;DR

LangChain's URL loader checked if a URL was safe before fetching it, but let the fetch client automatically follow redirects to unsafe places. Attackers could use a 'safe' URL that redirects to 169.254.169.254 to steal cloud credentials.

⚠️ Exploit Status: POC

Technical Details

  • CWE ID: CWE-918
  • Attack Vector: Network
  • CVSS: 4.1 (Medium)
  • Impact: Information Disclosure
  • Exploit Status: PoC Available
  • Patch Status: Released (v1.1.18)

Affected Systems

  • @langchain/community
  • @langchain/community: < 1.1.18 (Fixed in: 1.1.18)

Code Analysis

Commit: 2812d2b

Fix: handle redirects manually to prevent SSRF bypass

fetch(currentUrl, { redirect: "manual" })
Enter fullscreen mode Exit fullscreen mode

Exploit Details

  • GitHub: Unit tests in the fix commit serve as a functional PoC for the redirect bypass.

Mitigation Strategies

  • Upgrade @langchain/community to patched versions.
  • Network-level egress filtering to block metadata services.
  • Run LLM workers in isolated containers/VPCs.

Remediation Steps:

  1. Identify projects using @langchain/community < 1.1.18.
  2. Run npm install @langchain/community@latest or yarn upgrade @langchain/community.
  3. Verify that node_modules/@langchain/community/package.json shows version 1.1.18+.
  4. Review firewall rules to ensure 169.254.169.254 is blocked for application containers.

References

Read the full report for CVE-2026-27795 on our website for more details including interactive diagrams and full exploit analysis.

Top comments (0)