CVE-2026-26019 is a Server-Side Request Forgery (SSRF) vulnerability found in the RecursiveUrlLoader class of the langchainjs framework, specifically in versions before 1.1.14. LangChain is a popular framework for building applications powered by large language models (LLMs). The RecursiveUrlLoader is a web crawler designed to recursively follow links starting from a base URL, with an option called preventOutside enabled by default to restrict crawling to the same domain. However, the implementation uses a simplistic string prefix check (String.startsWith) to enforce this restriction, which does not perform semantic URL validation. This flaw allows an attacker who controls content on a page being crawled to embed links that appear to share the same prefix but actually point to attacker-controlled domains or internal infrastructure. Furthermore, the crawler does not validate whether URLs resolve to private or reserved IP addresses, such as localhost, RFC 1918 addresses, or cloud metadata service endpoints. Consequently, the crawler may inadvertently fetch sensitive internal resources or metadata, potentially exposing confidential information or enabling further attacks. The vulnerability requires low privileges (PR:L) and user interaction (UI:R), with network attack vector (AV:N), and impacts confidentiality (C:L) but not integrity or availability. The scope is changed (S:C) because the attacker can cause the crawler to access resources outside the intended domain. No known exploits are reported in the wild as of publication. The issue was addressed in langchainjs version 1.1.14 by improving URL validation and restricting crawler behavior. This vulnerability is particularly relevant for organizations deploying LLM applications that use langchainjs to crawl web content, as it could lead to unauthorized internal resource access or data leakage.

For European organizations, this SSRF vulnerability poses a risk of unauthorized access to internal network resources, cloud metadata services, and potentially sensitive infrastructure. Organizations using langchainjs versions prior to 1.1.14 in their LLM-powered applications may inadvertently expose internal services or cloud credentials if the crawler follows maliciously crafted links. This could lead to information disclosure, such as internal IP addresses, configuration details, or cloud instance metadata, which attackers could leverage for further attacks like privilege escalation or lateral movement. The impact is heightened in sectors with strict data protection requirements (e.g., finance, healthcare, government) where internal network confidentiality is critical. Additionally, organizations relying on cloud providers with metadata services accessible via SSRF are at risk of credential theft or unauthorized cloud resource access. Although the CVSS score is medium, the potential for internal reconnaissance and data leakage makes this a significant concern for European enterprises deploying vulnerable langchainjs versions.

The primary mitigation is to upgrade langchainjs to version 1.1.14 or later, where the vulnerability is fixed by implementing proper semantic URL validation and restricting crawler behavior. Organizations should audit their use of RecursiveUrlLoader and ensure the preventOutside option is correctly enforced. Additionally, implement network-level controls such as firewall rules or egress filtering to block crawler requests to private IP ranges (e.g., 10.0.0.0/8, 192.168.0.0/16, 172.16.0.0/12), localhost addresses, and cloud metadata IPs (e.g., 169.254.169.254). Employ application-layer validation to whitelist allowed domains and reject suspicious URLs before crawling. Monitoring crawler logs for unusual outbound requests can help detect exploitation attempts. Where possible, isolate crawling components in segmented network zones with limited access to internal resources. Finally, educate developers and security teams about SSRF risks in LLM application components and integrate secure coding practices for URL handling.