CVE-2026-55455: Appsmith

Critical severity, CVSS 9.1. EPSS: 0.4% chance of exploitation in the next 30 days.

Appsmith is a platform to build admin panels, internal tools, and dashboards. Prior to 2.1, the outbound HTTP host filter applied by WebClientUtils (used by the REST API and GraphQL datasource plugins) validates hosts against an exact-match string denylist. The comprehensive address-class check (loopback, any-local, link-local, fc00::/7) exists only on a separate code path used by SMTP, not by the HTTP plugin path. As a result, an authenticated user can craft outbound requests that reach loopback-bound services inside the container. This vulnerability is fixed in 2.1.

Affected products

• Appsmith Appsmith: before 2.1 (fixed in 2.1)

Published 2026-06-24. Last modified 2026-06-26.