CVE-2026-55455: Appsmith: SSRF in REST API / GraphQL datasource plugins via insufficient host denylist

Severity: critical (CVSS 9.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-24 · updated 2026-10-25
Weakness: CWE-918

Description

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

appsmithorg appsmith: before 2.1 — fixed in 2.1

How to fix

Upgrade to a fixed version: appsmithorg appsmith 2.1. Check the vendor advisory for mitigations.

References

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