CVE-2026-101049

Executive Summary

CVE-2026-101049 is an improper authentication vulnerability (CWE-287) in the Heym workflow automation platform affecting versions before 0.0.53. The product fails to verify Slack request signatures for trigger nodes that lack credential IDs or possess empty signing secrets, allowing remote unauthenticated attackers who know or guess a webhook URL to inject forged Slack events. Successful exploitation triggers workflow execution using the workflow owner's stored credentials, enabling unauthorized actions within connected third-party services (CVSS 6.5, Integrity: High).

Technical Analysis

The vulnerability resides in Heym's Slack webhook trigger handling logic. Slack's inbound webhook model relies on HMAC-SHA256 request signatures (delivered in the X-Slack-Signature header alongside X-Slack-Request-Timestamp) that the receiving application must validate against a shared signing secret to prove that an incoming event genuinely originated from Slack. Heym's trigger node implementation associates a signing secret with a credential record referenced by credential ID. When a trigger node is configured without a credential ID, or when the referenced credential contains an empty signing secret, the signature verification step is effectively skipped rather than failing closed. The result is an unauthenticated trust boundary: any HTTP client capable of reaching the trigger node's webhook URL can post an arbitrary JSON payload formatted as a Slack event and have it accepted as legitimate.

The flaw is a classic fail-open authentication defect. The root cause is the absence of a mandatory "deny by default" check when no secret material is available for comparison. Secure implementations must reject unsigned or unverifiable requests whenever the signing secret is missing or empty; Heym prior to 0.0.53 instead proceeds to event processing. Because the vulnerability is network-reachable (AV:N), requires no prior authentication (PR:N), and needs no user interaction (UI:N), it is attractive for opportunistic abuse, though the AC:H rating reflects practical constraints: the attacker must know or discover the specific webhook URL path, which is not enumerated by the product and functions as a weak shared secret.

The CVSS v3.1 subscores confirm a targeted-integrity impact: Confidentiality: Low (workflow execution may surface limited data through downstream effects), Integrity: High (workflows execute with the owner's credentials, allowing actions such as sending messages, creating records, or invoking connected APIs), and Availability: None. CWE-287 (Improper Authentication) accurately characterizes the defect class. Note that CVE metadata does not enumerate the specific internal function, route, or parameter implementing the check; no vendor advisory text beyond the description was available at analysis time, and no public proof-of-concept or exploit code exists, so the attack chain below is inferred strictly from the vulnerability class.

Exploitation Scenarios

No public PoC is available; the following attack chain is inferred from the vulnerability class (improper authentication / failed signature verification).

1. Reconnaissance and target identification. The attacker identifies internet-exposed Heym instances, for example via HTTP fingerprinting of the Heym UI or known workflow-automation artifacts. The critical asset is the Trigger node's webhook URL, which Heym exposes as a unique, hard-to-guess path. Attackers may obtain it through leaked documentation, screenshots, source repositories, logs, or by brute-forcing predictable path segments where deployments use weak or reused identifiers.

2. Triggering the flaw. The attacker crafts an HTTP POST request to the target webhook URL containing a body shaped like a Slack event payload (for example, an event_callback envelope). Because the associated trigger node has no credential ID or an empty signing secret, Heym does not validate the Slack request signature headers. The forged request is therefore accepted as an authentic Slack event with no valid X-Slack-Signature required.

3. Payload and execution method. The attacker delivers JSON that matches the trigger node's expected event schema so that the workflow's matching conditions are satisfied. The event fields are attacker-controlled, meaning the data flowing into the workflow — and thus into any downstream nodes (API calls, messaging actions, ticket creation, database writes) — is fully attacker-influenced. No authentication credential is needed at this stage because the signature gate is bypassed.

4. Post-exploitation impact. The workflow executes within the owner's authenticated context, using the owner's stored third-party credentials. Depending on workflow logic, consequences include unauthorized outbound actions (message posting, data exfiltration to attacker-controlled destinations), creation or modification of records in connected services, or chaining into further automation steps. Confidentiality impact is limited but non-zero; integrity impact is high. Persistence would require modifying workflow definitions, which is not established by this CVE and should not be assumed.

Impact Assessment

Affected systems are self-hosted or cloud Heym deployments running versions before 0.0.53 that expose Slack trigger webhooks and have at least one trigger node configured without a credential ID or with an empty signing secret. The blast radius extends beyond Heym itself to every third-party service whose credentials are attached to reachable workflows — Slack workspaces, ticketing systems, CRMs, CI/CD integrations, and any API reachable by workflow nodes. Because workflows routinely hold privileged OAuth tokens, a single forged event can translate into privileged actions in systems the Heym operator considers trusted.

Business impact centers on integrity and trust: forged events can trigger business processes (approvals, notifications, record changes, refunds, provisioning) that appear legitimate to downstream audit systems. CVSS subscores quantify this as Integrity: High, with Confidentiality: Low and Availability: None, yielding a 6.5 Medium base score. The AC:H metric reflects the requirement to know the webhook URL; however, in environments where webhook paths leak through repositories or shared documentation, effective exploitability rises. Multi-tenant or internet-facing deployments with many workflows represent the highest-risk profile. No CISA KEV listing and no EPSS score exist as of analysis, indicating no observed mass exploitation, but the fail-open nature of the defect makes it a durable, low-effort target for targeted actors once a URL is known.

Detection Guidance

Sigma Rule

title: Suspicious Slack Webhook Event Without Valid Signature (Heym CVE-2026-101049)
id: 7b1e9f2a-3c4d-4e5f-9a10-2b6c7d8e9f01
status: experimental
description: Detects inbound requests to Heym Slack trigger webhook endpoints that lack a valid Slack signature header, consistent with forged event injection in Heym < 0.0.53.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-101049
author: valtersit.com Threat Intelligence
date: 2026/01/01
logsource:
  category: webserver
detection:
  selection_path:
    cs-uri-path|contains:
      - '/webhook'
      - '/slack'
      - '/trigger'
  selection_ua:
    cs-user-agent|contains: 'Slackbot'
  selection_missing_sig:
    cs-uri-query|contains: 'X-Slack-Signature'
  condition: selection_path and not selection_missing_sig
fields:
  - c-ip
  - cs-uri-path
  - cs-method
  - cs-user-agent
falsepositives:
  - Health checks or administrative requests hitting webhook paths
level: medium

YARA Rule

rule CVE_2026_101049_Heym_Slack_Trigger_Auth_Bypass
{
    meta:
        description = "Detects Heym source or configuration files lacking mandatory Slack signing secret verification, context for CVE-2026-101049"
        author = "valtersit.com Threat Intelligence"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-101049"
        date = "2026-01-01"
        severity = "medium"

    strings:
        $s1 = "X-Slack-Signature" ascii nocase
        $s2 = "signingSecret" ascii nocase
        $s3 = "signing_secret" ascii nocase
        $s4 = "credentialsId" ascii nocase
        $s5 = "slack" ascii nocase
        $s6 = "event_callback" ascii

    condition:
        uint16(0) == 0x0A0D or filesize < 10MB and
        (($s1 and $s2) or ($s1 and $s3)) and $s5 and
        (any of ($s4) or any of ($s6))
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-101049 Heym Slack Forged Webhook Event (Missing Signature)"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"slack"; nocase; http.uri; content:"trigger"; nocase; content:"event_callback"; http_client_body; nocase; content:"X-Slack-Signature"; http_header; nocase; negate; sid:2026101049; rev:1; reference:cve,2026-101049; classtype:attempted-admin;)

Elastic Detection

sequence by source.ip with maxspan=30s
  [ network where http.request.method == "POST" and
      http.request.body.content : "event_callback" and
      http.request.body.content : "slack" ]
  [ network where http.request.method == "POST" and
      not http.request.headers.X-Slack-Signature : "*" ]

Splunk SPL Query

index=web sourcetype=access_combined OR sourcetype=heym
method=POST uri_path="*slack*" 
NOT http_request_headers_X_Slack_Signature=*
| stats count min(_time) as first_seen max(_time) as last_seen by clientip uri_path
| where count > 0
| table first_seen last_seen clientip uri_path count
| sort - count

Wazuh OSSEC Rule

<group name="web,appsec,heym,">
  <rule id="101049" level="10">
    <decoded_as>json</decoded_as>
    <field name="request.method">POST</field>
    <field name="url.path">webhook|slack|trigger</field>
    <field name="request.headers.X-Slack-Signature" negate="yes">.+</field>
    <description>CVE-2026-101049 - Possible Heym Slack webhook forged event (missing Slack signature header)</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate mitigations. Remove or isolate Slack trigger nodes that lack a credential ID or whose signing secret is empty, and populate every Slack trigger with a valid, non-empty signing secret so that signature verification is enforced. Where an unconfigurable trigger must remain, restrict the webhook URL at the network layer (WAF, reverse proxy, or IP allowlisting limited to Slack's published egress ranges) and rotate the webhook path so that previously exposed URLs become unusable. Rotate any third-party credentials attached to workflows reachable by these triggers, and audit recent workflow execution logs for events that lack corresponding Slack-originated activity.

2. Patch/upgrade steps. Upgrade Heym to 0.0.53 or later, which is documented as the fixed release. Because no vendor advisory, commit, or OSV package record was available at analysis time, operators should verify the release directly from the upstream project, confirm the changelog references signature verification enforcement, and stage the upgrade in a non-production environment before rolling out. After upgrade, re-verify that all Slack triggers reject requests bearing absent or mismatched signatures.

3. Long-term hardening. Adopt fail-closed authentication defaults for all inbound trigger endpoints — required signature or shared-secret validation with no optional bypass. Enforce defense-in-depth for webhook receivers: TLS-only listeners, strict schema validation of incoming event bodies, replay protection using Slack's timestamp tolerance window, and rate limiting on webhook paths. Segment workflow engine networks from sensitive internal services, apply least-privilege scoping to every stored third-party credential, and monitor workflow execution with the detections in this report. Maintain an inventory of every trigger node with its authentication posture and review it on each platform upgrade.

References

• NVD — CVE-2026-101049: https://nvd.nist.gov/vuln/detail/CVE-2026-101049
• CWE-287 — Improper Authentication: https://cwe.mitre.org/data/definitions/287.html
• Slack — Verifying requests from Slack (signature verification guidance): https://api.slack.com/authentication/verifying-requests-from-slack
• CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• FIRST EPSS: https://www.first.org/epss/ (no score assigned at analysis time)

No public proof-of-concept, exploit code, Nuclei template, or threat actor campaign has been associated with CVE-2026-101049 as of this writing; the vulnerability is not listed in CISA KEV.