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AppsmithApplication

CVE-2026-55455

CRITICAL · 9.1 CVSS v3.1 Published 2026-06-24
Fix available
A fix is available. Upgrade to 2.1 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click 8 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Appsmith's WebClientUtils applies an insufficient host filter to outbound HTTP requests from REST API and GraphQL datasource plugins. The HTTP plugin path uses only an exact-match string denylist instead of comprehensive address-class validation (loopback, link-local, fc00::/7) that exists in the separate SMTP code path. This allows authenticated users to craft requests reaching internal loopback-bound services within the container.

MitigationUpgrade to Appsmith version 2.1 or later, which implements comprehensive address-class validation for outbound HTTP requests to prevent SSRF attacks against internal services.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
AppsmithApplication
Affected:< 2.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Appsmith version
    Check the version.yaml file in the Appsmith installation directory, or look at the footer of the Appsmith UI which displays the running version number.
    Affected if The displayed version is less than 2.1 (e.g., 2.0.x, 1.x.x)
  2. Locate WebClientUtils implementation
    Inspect the source code or JAR files for the class 'WebClientUtils' in the backend installation. Search for methods handling outbound HTTP requests from datasource plugins.
    Affected if The code uses an exact-match string denylist for host filtering rather than address-class validation (checking for loopback 127.0.0.0/8, link-local 169.254.0.0/16, IPv6 fc00::/7)
  3. Check REST API datasource configuration
    Navigate to the Admin Settings > Datasources section in the Appsmith UI, or inspect the database table for datasources. Look for any REST API datasources created by users.
    Affected if Any REST API datasources exist and the WebClientUtils uses denylist-only filtering (exact string matches)
  4. Check GraphQL datasource configuration
    Navigate to Admin Settings > Datasources in the Appsmith UI, or query the datasource database table. Look for any GraphQL datasources.
    Affected if Any GraphQL datasources exist and the WebClientUtils lacks comprehensive address-class validation
  5. Verify SMTP path host validation exists
    Locate the SMTP-related code path in WebClientUtils and confirm it implements proper address-class validation (loopback, link-local, IPv6 private ranges). Compare this to the HTTP plugin path.
    Affected if SMTP path validates address classes but HTTP/REST/GraphQL paths use only string denylists

You are affected if running Appsmith version < 2.1 with REST API or GraphQL datasources configured, and the WebClientUtils lacks comprehensive address-class validation for outbound HTTP requests.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 2.1 or later
Fixed in 2.1
Interim mitigation

Upgrade to Appsmith version 2.1 or later, which implements comprehensive address-class validation for outbound HTTP requests to prevent SSRF attacks against internal services.

Recommended fix High confidence

Appsmith 2.1

  1. Upgrade Appsmith to version 2.1 or later to obtain the fixed WebClientUtils with comprehensive address-class validation (loopback, any-local, link-local, fc00::/7)
  2. After upgrade, verify the REST API and GraphQL datasource plugins now use the protected code path with proper host filtering
  3. Confirm that outbound HTTP requests are now validated against address classes rather than just an exact-match denylist
Caveat Review release notes for 2.1 to check for any breaking changes in REST API, GraphQL, or datasource plugins before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Appsmith Scoped from the published advisory
  • Consultation8.0 h
  • Implementation16.0 h
  • Testing12.0 h
  • Review / QA8.0 h
44.0 hours of engineering $7,720
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $12,352.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-55455 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data