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CVE-2026-101049 – Authentication Bypass via Slack Webhook Signature Verification Failure – Heym befo

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Summary

CVE-2026-101049 is an improper authentication vulnerability (CWE-287) in Heym, a self-hosted workflow automation platform, affecting all versions prior to 0.0.53. When a workflow’s Slack Trigger node is configured without a credential ID or with an empty signing secret, Heym fails to verify Slack request signatures, allowing a remote, unauthenticated attacker who knows the public webhook URL to forge Slack events and trigger the workflow using the owner’s stored credentials. The issue carries a CVSS v4.0 base score of 8.3 (High).

Technical details

  • Root cause: The Slack Trigger node is designed to verify inbound webhook requests using HMAC-SHA256 signature validation against a Slack signing secret. When no slack_trigger credential is assigned to the node, or the assigned credential has an empty signing secret, Heym’s verification logic fails open instead of rejecting the request.
  • Trigger conditions: A workflow must expose a Slack Trigger node whose credential ID is unset or whose signing secret field is blank — a state the vendor’s own documentation describes as intended "only for local testing," but which is not blocked in production deployments.
  • Attack vector: Network — an attacker only needs to know or discover the workflow’s public Slack webhook URL; no authentication, credentials, or user interaction are required.
  • Impact: By sending crafted, unsigned requests that mimic Slack Events API payloads, an attacker can invoke the affected workflow, causing it to execute with the privileges and credentials of the workflow’s owner. This can lead to unauthorized workflow execution and downstream actions (e.g., data access, integration calls) performed under the victim’s stored credentials.

Affected software

  • Vendor/Product: heymrun / Heym
  • Vulnerable versions: All versions prior to 0.0.53
  • Fixed version: 0.0.53 and later

Severity

  • CVSS v4.0: 8.3 (High) — CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:H/VA:N/SC:N/SI:N/SA:N
  • CVSS v3.1: 6.5 (Medium) — CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N
  • CWE-287: Improper Authentication

Mitigation and recommended actions

  • Immediate: Upgrade Heym to version 0.0.53 or later, which addresses the fail-open signature verification behavior.
  • Configuration check: Ensure every Slack Trigger node in use has a valid slack_trigger credential assigned with a non-empty signing secret retrieved from the corresponding Slack App configuration; never rely on the no-credential mode outside of isolated local testing.
  • If immediate patching is not possible: Restrict or firewall access to workflow webhook endpoints so they are not reachable from untrusted networks, audit existing workflows for Slack Trigger nodes lacking a credential, and disable or reconfigure any such workflows until the signing secret is set and the platform is patched.
  • Post-patch validation: After upgrading, confirm that unsigned or improperly signed requests to Slack webhook endpoints are rejected.

References

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