Link Preview JS extracts web links information. Prior to 4.0.4, the resolveDNSHost mitigation in index.ts validates one resolved IP address but fetches the original hostname, allowing an attacker-controlled DNS server to return a public address during validation and a loopback or internal address during the final connection. This DNS rebinding condition bypasses the SSRF protection and can cause the server-side preview fetch to reach internal HTTP resources. Redirect handling is affected by the same validation-to-fetch mismatch. This issue is fixed in version 4.0.4.

Affected: npm: link-preview-js

The existing advisory GHSA-4gp8-rjrq-ch6q / CVE-2026-43897 states that the SSRF issue was fixed in 4.0.1. However, 4.0.3 remains bypassable when the documented resolveDNSHost mitigation is used.

Root cause: The library validates one resolved IP address through resolveDNSHost, but later performs fetch() against the original hostname without pinning the connection to the validated IP. An attacker-controlled DNS server can return a public IP during validation and a loopback/internal IP during the final connection.

Impact: This allows an attacker to bypass the documented SSRF mitigation and make the server-side fetch reach loopback or internal addresses under DNS rebinding conditions.

This appears to be either an incomplete fix for CVE-2026-43897 or a new DNS rebinding SSRF bypass affecting the latest version.

The PoC was reproduced in a local-only controlled environment to avoid targeting production or third-party systems. Evidence and reproduction details can be provided privately.