CVE-2026-45796: Coder Unauthenticated SSRF Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-686c-7vgv-v3fx",
  "modified" : "2026-05-19T19:53:51Z",
  "published" : "2026-05-19T19:53:51Z",
  "aliases" : [ "CVE-2026-45796" ],
  "summary" : "Coder: Unauthenticated SSRF via Azure Instance Identity Endpoint",
  "details" : "## Summary\n\nUnauthenticated semi-blind Server-Side Request Forgery (SSRF) via the Azure instance identity endpoint (`POST /api/v2/workspaceagents/azure-instance-identity`). An external attacker can force the Coder server to issue HTTP GET requests to arbitrary internal or external hosts by submitting a crafted PKCS#7 signature. The server does not return the target's response body, but error messages in the API response reveal whether the target is reachable and what type of failure occurred.\n\n## Details\n\nThe `POST /api/v2/workspaceagents/azure-instance-identity` endpoint accepts a PKCS#7 signature without authentication. During certificate chain verification, [`azureidentity.Validate()`](https://github.com/coder/coder/blob/aa0e288b88/coderd/azureidentity/azureidentity.go#L83-L88) iterates over the signer certificate's `IssuingCertificateURL` extension and fetches each URL using `http.DefaultClient` with no host restriction, no private-IP blocking, and no response-size limit.\n\nAn attacker crafts a self-signed certificate whose Common Name matches `*.metadata.azure.com` (passing the `allowedSigners` regex) and whose `IssuingCertificateURL` points to an attacker-chosen target. The server fetches that URL and feeds the response body into `x509.ParseCertificate`. The parsed result is discarded, but the wrapped error string is returned verbatim in the JSON response via `Detail: err.Error()`. Connection-level errors (\"connection refused\", \"i/o timeout\", DNS failures) and certificate-parse errors give the attacker enough signal to infer host reachability and port state without seeing the actual response content.\n\n**Root causes:**\n\n1. No allowlist on `IssuingCertificateURL` hosts. Any URL was accepted.\n2. `http.DefaultClient` was used. It follows redirects and connects to private, link-local, and loopback addresses.\n3. Unbounded `io.ReadAll` on the response body (memory exhaustion vector).\n4. Raw `err.Error()` was returned in the JSON response, leaking internal HTTP client errors to the caller.\n\n## Impact\n\nThis is a semi-blind SSRF: the server makes the outbound request but the HTTP response body is consumed by `x509.ParseCertificate` and never returned to the attacker.\n\n- **Internal network reconnaissance.** The attacker can map internal hosts and ports by observing error differentiation in the API response: \"connection refused\" (port closed), \"i/o timeout\" (host unreachable or firewalled), DNS failure (host does not exist), or certificate-parse error (port open and responding). This enables systematic scanning of the internal network from the Coder server's vantage point.\n- **Requests to sensitive endpoints.** The server can be directed to hit cloud metadata services (e.g. `http://169.254.169.254/`), internal admin interfaces, or other services. The attacker cannot read the response content, but the request itself may have side effects depending on the target.\n- **Error-based information disclosure.** Wrapped Go HTTP client errors in the `Detail` field expose internal hostnames, IP addresses, port numbers, and network topology details.\n- **Memory exhaustion.** The unbounded `io.ReadAll` on the response body allows an attacker to point `IssuingCertificateURL` at a large resource, forcing the server to buffer it entirely in memory.\n\n## Patches\n\nFixed in [#25274](https://github.com/coder/coder/pull/25274) (commit [`57b11d405`](https://github.com/coder/coder/commit/57b11d405f17492aa789d4b9ff33366f961a37f8)):\n\nThe fix was backported to all supported release lines:\n\n| Release line | Patched version |\n|---|---|\n| 2.33 | [v2.33.3](https://github.com/coder/coder/releases/tag/v2.33.3) |\n| 2.32 | [v2.32.2](https://github.com/coder/coder/releases/tag/v2.32.2) |\n| 2.31 | [v2.31.12](https://github.com/coder/coder/releases/tag/v2.31.12) |\n| 2.30 | [v2.30.8](https://github.com/coder/coder/releases/tag/v2.30.8) |\n| 2.29 | [v2.29.13](https://github.com/coder/coder/releases/tag/v2.29.13) |\n| 2.24 (ESR) | [v2.24.5](https://github.com/coder/coder/releases/tag/v2.24.5) |\n\n## Workarounds\n\nIf the Azure identity-auth mechanism is not being used then restrict access to the corresponding endpoint (`/api/v2/workspaceagents/azure-instance-identity`) using ingress firewall and/or proxy ACLs.\n\n### Recognition\n\nWe'd like to thank [Ben Tran](https://github.com/bencalif) of [calif.io](http://calif.io/) and Anthropic's Security Team (`ANT-2026-22447`) for independently disclosing this issue!",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/coder/coder/v2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.33.0-rc.0"
      }, {
        "fixed" : "2.33.3"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/coder/coder/v2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.32.0-rc.0"
      }, {
        "fixed" : "2.32.2"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/coder/coder/v2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.31.0"
      }, {
        "fixed" : "2.31.12"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/coder/coder/v2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.30.0"
      }, {
        "fixed" : "2.30.8"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/coder/coder/v2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.29.0"
      }, {
        "fixed" : "2.29.13"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/coder/coder/v2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.24.5"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/coder/coder"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "0.27.3"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/coder/coder/security/advisories/GHSA-686c-7vgv-v3fx"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/coder/coder/pull/25274"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/coder/coder/commit/57b11d405f17492aa789d4b9ff33366f961a37f8"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/coder/coder"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/coder/coder/releases/tag/v2.24.5"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/coder/coder/releases/tag/v2.29.13"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/coder/coder/releases/tag/v2.30.8"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/coder/coder/releases/tag/v2.31.12"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/coder/coder/releases/tag/v2.32.2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/coder/coder/releases/tag/v2.33.3"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-918" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-19T19:53:51Z",
    "nvd_published_at" : null
  }
}