GHSA-mhc4-qq83-fmrr: axonflow-sdk-go Webhook Signing-key (HMAC-SHA256) Not Exposed Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mhc4-qq83-fmrr",
  "modified" : "2026-05-06T23:15:38Z",
  "published" : "2026-05-06T23:15:38Z",
  "aliases" : [ ],
  "summary" : "axonflow-sdk-go: Webhook signing-key (HMAC-SHA256) not exposed by SDK type, preventing signature verification",
  "details" : "## Summary\n\nThe AxonFlow SDK's `WebhookSubscription` (or equivalent) type did not expose the HMAC-SHA256 signing key returned by the platform's `CreateWebhook` endpoint. Without access to the secret through the typed SDK API, callers had no path to verify the `X-AxonFlow-Signature` header on incoming webhook deliveries. Affected callers had two unsatisfactory options:\n\n1. Skip signature verification entirely — accepting any payload from any source that knew the webhook URL.\n2. Hand-parse the raw HTTP JSON response to extract the secret, bypassing the type-safe SDK surface.\n\nThis advisory is filed across all four AxonFlow SDKs (Go, Python, TypeScript, Java) because the same defect and the same fix landed in each.\n\n## Affected versions\n\nVersions 5.6.1 and below.\n\n## Impact\n\nA webhook receiver using the SDK's typed API to handle inbound deliveries had no path to authenticate the source of incoming payloads. An attacker who learned the webhook URL — through misconfiguration, log leakage, observable network traffic during setup, or any other discovery channel — could forge webhook deliveries indistinguishable from legitimate ones, causing the receiving application to act on fabricated events (e.g. simulated approval-granted callbacks, simulated policy-decision callbacks, simulated step-completion callbacks).\n\n## Remediation\n\nUpgrade to the patched version listed in Vulnerabilities below. The signing key is now exposed on the `WebhookSubscription` response type returned by `CreateWebhook`. Implementations should:\n\n1. Persist the secret returned by `CreateWebhook` securely (it is only returned once, at create time).\n2. On each incoming webhook delivery, compute `HMAC-SHA256(secret, raw_body)` and compare it in constant time against the `X-AxonFlow-Signature` header.\n3. Reject any delivery whose signature does not match.\n\n## Credit\n\nIdentified by AxonFlow internal security review during the April 2026 quality-freeze epic.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/getaxonflow/axonflow-sdk-go/v5"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "5.7.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/getaxonflow/axonflow-sdk-go/security/advisories/GHSA-mhc4-qq83-fmrr"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/getaxonflow/axonflow-sdk-go"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-345", "CWE-347" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-06T23:15:38Z",
    "nvd_published_at" : null
  }
}