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Improper Signature VerificationWeakness · CWE-347

CVE-2026-42193

CRITICAL · 9.1 CVSS v3.1 Published 2026-05-08
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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
Plunk is an open-source email platform built on top of AWS SES. Prior to version 0.9.0, the /webhooks/sns endpoint accepts Amazon SNS notification payloads from unauthenticated requests without verifying the SNS signature, certificate, or topic ARN, meaning anyone can forge a valid-looking webhook request. This allows an unauthenticated attacker to spoof SNS events to trigger workflow automations, unsubscribe contacts, manipulate email delivery metrics, and potentially exhaust billing credits. This issue has been patched in version 0.9.0.

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

The /webhooks/sns endpoint in Plunk versions prior to 0.9.0 accepts Amazon SNS notifications without verifying the AWS signature, SSL certificate, or topic ARN, allowing unauthenticated attackers to forge valid-looking webhook payloads and manipulate email workflows, contacts, delivery metrics, and billing.

MitigationUpgrade to Plunk version 0.9.0 or later which implements proper SNS signature and topic verification.

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

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
None
Integrity
High
Availability
High

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

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 Plunk version
    Query the Plunk API version endpoint (commonly /api/version or check the package.json/VERSION file in the installation directory)
    Affected if The installed version is prior to 0.9.0 (e.g., 0.8.x, 0.7.x, etc.)
  2. Locate Plunk installation
    Identify the Plunk application directory and examine configuration files for SNS webhook settings (look for files containing 'sns', 'webhook', or 'amazon' keywords)
    Affected if Configuration files exist and show SNS webhook endpoint configuration without signature verification enabled
  3. Test SNS webhook endpoint accessibility
    Send a crafted HTTP request to http(s)://<plunk-host>/webhooks/sns and observe the response
    Affected if The endpoint responds (returns 200, 400, or other HTTP status rather than 404) indicating the endpoint exists and is reachable
  4. Inspect SNS webhook handler code
    Examine the backend code handling /webhooks/sns - look for signature verification functions (e.g., verify_signature, verify_sns_message) and topic ARN validation
    Affected if The code lacks or bypasses AWS signature verification, SSL certificate validation, and topic ARN checks

You are affected if running Plunk version 0.9.0 or earlier AND the /webhooks/sns endpoint is exposed without proper AWS SNS signature and topic verification implemented.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to Plunk version 0.9.0 or later which implements proper SNS signature and topic verification.

Recommended fix High confidence

Version 0.9.0

  1. 1. Identify the current version of Plunk being deployed in your environment
  2. 2. If running a version prior to 0.9.0, plan for upgrade to version 0.9.0 or later
  3. 3. Obtain the latest release from the official Plunk repository
  4. 4. Follow the project's upgrade instructions to apply version 0.9.0
  5. 5. After upgrade, verify that /webhooks/sns endpoint now properly verifies SNS signatures, certificates, and topic ARNs
  6. 6. Test that legitimate SNS webhook deliveries work correctly post-upgrade

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

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
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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-2026-42193 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