Summary A redirect-based Server-Side Request Forgery (SSRF) bypass exists in RecursiveUrlLoader in @langchain/community. The loader validates the initial URL but allows the underlying fetch to follow redirects automatically, which permits a transition from a safe public URL to an internal or metadata endpoint without revalidation. This is a bypass of the SSRF protections introduced in 1.1.14 (CVE-2026-26019).
Affected Component - Package: @langchain/community - Component: RecursiveUrlLoader - Configuration: preventOutside (default: true) is insufficient to prevent this bypass when redirects are followed automatically.
Description RecursiveUrlLoader is a web crawler that recursively follows links from a starting URL. The existing SSRF mitigation validates the initial URL before fetching, but it does not re-validate when the request follows redirects. Because fetch follows redirects by default, an attacker can supply a public URL that passes validation and then redirects to a private network address, localhost, or cloud metadata endpoint.
This constitutes a “check‑then‑act” gap in the request lifecycle: the safety check occurs before the redirect chain is resolved, and the final destination is never validated.
Impact If an attacker can influence content on a page being crawled (e.g., user‑generated content, untrusted external pages), they can cause the crawler to: - Fetch cloud instance metadata (AWS, GCP, Azure), potentially exposing credentials or tokens - Access internal services on private networks (10.x, 172.16.x, 192.168.x) - Connect to localhost services - Exfiltrate response data through attacker-controlled redirect chains
This is exploitable in any environment where RecursiveUrlLoader runs with access to internal networks or metadata services, which includes most cloud-hosted deployments.
Attack Scenario 1. The crawler is pointed at a public URL that passes initial SSRF validation. 2. That URL responds with a 3xx redirect to an internal target. 3. The fetch follows the redirect automatically without revalidation. 4. The crawler accesses the internal or metadata endpoint.
Example redirector: https://302.r3dir.me/--to/?url=http://169.254.169.254/latest/meta-data/
Root Cause - SSRF validation (validateSafeUrl) is only performed on the initial URL. - Redirects are followed automatically by fetch (redirect: "follow" default), so the request can change destinations without additional validation.
Resolution Upgrade to @langchain/community >= 1.1.18, which validates every redirect hop by disabling automatic redirects and re-validating Location targets before following them. - Automatic redirects are disabled (redirect: "manual"). - Each 3xx Location is resolved and validated with validateSafeUrl() before the next request. - A maximum redirect limit prevents infinite loops.
Reources - Original SSRF fix (CVE-2026-26019): enforced origin comparison and added initial URL validation - https://github.com/langchain-ai/langchainjs/security/advisories/GHSA-gf3v-fwqg-4vh7
Description
The RecursiveUrlLoader class in @langchain/community is a web crawler that recursively follows links from a starting URL. Its preventOutside option (enabled by default) is intended to restrict crawling to the same site as the base URL.
The implementation used String.startsWith() to compare URLs, which does not perform semantic URL validation. An attacker who controls content on a crawled page could include links to domains that share a string prefix with the target (e.g., https://example.com.attacker.com passes a startsWith check against https://example.com), causing the crawler to follow links to attacker-controlled or internal infrastructure.
Additionally, the crawler performed no validation against private or reserved IP addresses. A crawled page could include links targeting cloud metadata services (169.254.169.254), localhost, or RFC 1918 addresses, and the crawler would fetch them without restriction.
Impact
An attacker who can influence the content of a page being crawled (e.g., by placing a link on a public-facing page, forum, or user-generated content) could cause the crawler to:
- Fetch cloud instance metadata (AWS, GCP, Azure), potentially exposing IAM credentials and session tokens - Access internal services on private networks (10.x, 172.16.x, 192.168.x) - Connect to localhost services - Exfiltrate response data via attacker-controlled redirect chains
This is exploitable in any environment where RecursiveUrlLoader runs on infrastructure with access to cloud metadata or internal services — which includes most cloud-hosted deployments.
Resolution
Two changes were made:
1. Origin comparison replaced. The startsWith check was replaced with a strict origin comparison using the URL API (new URL(link).origin === new URL(baseUrl).origin). This correctly validates scheme, hostname, and port as a unit, preventing subdomain-based bypasses.
2. SSRF validation added to all fetch operations. A new URL validation module (@langchain/core/utils/ssrf) was introduced and applied before every outbound fetch in the crawler. This blocks requests to: - Cloud metadata endpoints: 169.254.169.254, 169.254.170.2, 100.100.100.200, metadata.google.internal, and related hostnames - Private IP ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 127.0.0.0/8, 169.254.0.0/16 - IPv6 equivalents: ::1, fc00::/7, fe80::/10 - Non-HTTP/HTTPS schemes (file:, ftp:, javascript:, etc.)
Cloud metadata endpoints are unconditionally blocked and cannot be overridden.
Workarounds
Users who cannot upgrade immediately should avoid using RecursiveUrlLoader on untrusted or user-influenced content, or should run the crawler in a network environment without access to cloud metadata or internal services.