CVE-2026-61554: Github.com/jm33 m0/emp3r0r/core Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-4595-rvpx-4q34",
  "modified" : "2026-09-15T20:47:17Z",
  "published" : "2026-09-15T20:47:17Z",
  "aliases" : [ "CVE-2026-61554" ],
  "summary" : "emp3r0r has an unauthenticated HTTP Polling DoS",
  "details" : "### Summary\nThe `http_poll` C2 transport accepts attacker-controlled HTTP polling sessions before CBOR `MsgAuth` authentication is completed. A remote unauthenticated attacker can create arbitrary polling sessions and send request bodies that are forwarded into the C2 dispatch path. This can consume server resources and trigger pre-auth C2 processing.\n\n### Details\nThe plain HTTP C2 server starts the HTTP polling listener and forwards requests into `HandleHTTPServerSession`:\n```go\n// core/internal/cc/server/c2_http_server.go\nmux.HandleFunc(c2Path, func(w http.ResponseWriter, req *http.Request) {\n    stream, err := transport.HandleHTTPServerSession(w, req, &live.RuntimeConfig.MalleableC2)\n    ...\n    if stream != nil {\n        go cborStreamAccept(transport.NewStreamTransport(stream, req.RemoteAddr))\n    }\n})\n```\nThe HTTP polling handler accepts an attacker-supplied `sessionID` and `init=1` cookie, then creates and stores a server-side stream before authentication:\n\n```go\n// core/internal/transport/c2channel_http.go\nif isInit {\n    stream = newHTTPServerStream(sessionID)\n    w.WriteHeader(http.StatusOK)\n    return stream, nil\n}\n```\nPOST bodies for that unauthenticated session are read and queued before CBOR authentication rejects them:\n```go\n// core/internal/transport/c2channel_http.go\ncase http.MethodPost:\n    data, err := io.ReadAll(req.Body)\n    if err == nil && len(data) > 0 {\n        select {\n        case stream.readCh <- data:\n            w.WriteHeader(http.StatusOK)\n        ...\n        }\n    }\n```\nAuthentication only happens later in the C2 dispatch layer:\n```go\n// core/internal/cc/server/dispatcher.go\nsecureConn := transport.NewSecureConn(t)\n...\nn, err := secureConn.Read(authFrame)\n```\n\n### PoC\n1. Start the C2 server in a lab environment with the HTTP polling transport exposed, for example with `--http-port 12345`.\n2. Send an unauthenticated HTTP POST to the default polling path `/api/v1/telemetry` with a random `sessionID` cookie and the `init=1` cookie value.\n3. Send a second unauthenticated HTTP POST to `/api/v1/telemetry` using the same `sessionID`, with a request body containing repeated `A` bytes.\n4. Observe that both unauthenticated requests return HTTP `200`.\n5. Observe the C2 server log showing attacker-controlled bytes reaching the encrypted C2 frame parser, for example: `read: invalid encrypted chunk length: 1094795585`.\n6. `1094795585` is `0x41414141`, which corresponds to `AAAA`, confirming unauthenticated request body data reached `cborProtocolDispatch` before CBOR `MsgAuth` authentication.\n7. Repeat the request sequence concurrently to increase server resource usage and log volume.\n\n### Impact\n- Remote unauthenticated attackers can create arbitrary HTTP polling sessions.\n- Attacker-controlled request bodies reach pre-auth C2 dispatch handling.\n- Repeated requests can consume server memory, goroutines, request handling capacity, and log volume.\n- C2 service availability and operator reliability may be degraded under sustained traffic.\n\n### Remediation\n- Require authentication before creating long-lived HTTP polling sessions.\n- Do not forward request bodies into the C2 stream before validation.\n- Add strict request body limits.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/jm33-m0/emp3r0r/core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.0.0-20260531142011-aed3d81641ab"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/jm33-m0/emp3r0r/security/advisories/GHSA-4595-rvpx-4q34"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/jm33-m0/emp3r0r"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jm33-m0/emp3r0r/releases/tag/v4.2.5"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-15T20:47:17Z",
    "nvd_published_at" : null
  }
}