{"id":"CVE-2026-61554","aliases":["EUVD-2026-79996","GHSA-4595-rvpx-4q34","GO-2026-6487"],"status":"published","title":"emp3r0r has an unauthenticated HTTP Polling DoS","description":"emp3r0r is a C2 designed by Linux users for Linux environments. Prior to version 4.2.5, the `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. Version 4.2.5 patches the issue.","severity":{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.00707,"percentile":0.53722,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-400"],"published":"2026-09-15T20:47:17Z","modified":"2026-10-28T02:31:06Z","fixes":[{"ecosystem":"Go","package":"github.com/jm33-m0/emp3r0r/core","fixed_in":["0.0.0-20260531142011-aed3d81641ab"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"Go","package":"github.com/jm33-m0/emp3r0r/core","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.0.0-20260531142011-aed3d81641ab"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/jm33-m0/emp3r0r/core","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.0.0-20260531142011-aed3d81641ab"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/jm33-m0/emp3r0r/core","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.0.0-20260531142011-aed3d81641ab"}]}]}],"products":[{"vendor":"jm33-m0","product":"emp3r0r"}],"references":[{"url":"https://github.com/jm33-m0/emp3r0r/security/advisories/GHSA-4595-rvpx-4q34","tags":["x_refsource_CONFIRM","exploit","advisory","web"]},{"url":"https://github.com/jm33-m0/emp3r0r/releases/tag/v4.2.5","tags":["x_refsource_MISC","web"]},{"url":"https://github.com/advisories/GHSA-4595-rvpx-4q34"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/61xxx/CVE-2026-61554.json","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-61554","tags":["advisory"]},{"url":"https://github.com/jm33-m0/emp3r0r","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-61554","title":"emp3r0r has an unauthenticated HTTP Polling DoS","description":"emp3r0r is a C2 designed by Linux users for Linux environments. Prior to version 4.2.5, the `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. Version 4.2.5 patches the issue.","status":"published","published":"2026-09-15T20:48:05.156Z","modified":"2026-09-16T17:59:54.763Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"cna"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T14:19:53.786088Z"}],"euvd":[{"id":"EUVD-2026-79996","description":"emp3r0r is a C2 designed by Linux users for Linux environments. Prior to version 4.2.5, the `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. Version 4.2.5 patches the issue.","status":"published","published":"2026-09-15T20:48:05Z","modified":"2026-09-16T17:59:54Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"updated_at":"2026-11-02T17:28:14.682482Z"}],"ghsa":[{"id":"GHSA-4595-rvpx-4q34","title":"emp3r0r has an unauthenticated HTTP Polling DoS","description":"### 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, \u0026live.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 \u0026\u0026 len(data) \u003e 0 {\n        select {\n        case stream.readCh \u003c- 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.","status":"published","published":"2026-09-15T20:47:17Z","modified":"2026-09-15T20:47:18Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T14:41:17.136201Z"}],"nvd":[{"id":"CVE-2026-61554","description":"emp3r0r is a C2 designed by Linux users for Linux environments. Prior to version 4.2.5, the `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. Version 4.2.5 patches the issue.","status":"published","published":"2026-09-15T21:16:41.223Z","modified":"2026-09-30T17:51:56.193Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"secondary"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T14:12:48.287983Z"}],"osv":[{"id":"CVE-2026-61554","title":"emp3r0r has an unauthenticated HTTP Polling DoS","description":"emp3r0r is a C2 designed by Linux users for Linux environments. Prior to version 4.2.5, the `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. Version 4.2.5 patches the issue.","status":"published","published":"2026-09-15T20:48:05.156Z","modified":"2026-10-28T02:31:06.761769281Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T15:45:12.933503Z"},{"id":"GHSA-4595-rvpx-4q34","title":"emp3r0r has an unauthenticated HTTP Polling DoS","description":"### 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, \u0026live.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 \u0026\u0026 len(data) \u003e 0 {\n        select {\n        case stream.readCh \u003c- 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.","status":"published","published":"2026-09-15T20:47:17Z","modified":"2026-09-28T17:10:43.770059304Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T15:46:36.434231Z"},{"id":"GO-2026-6487","title":"emp3r0r has an unauthenticated HTTP Polling DoS in github.com/jm33-m0/emp3r0r/core","description":"emp3r0r has an unauthenticated HTTP Polling DoS in github.com/jm33-m0/emp3r0r/core","status":"published","published":"2026-09-28T16:43:40Z","modified":"2026-09-28T17:00:16.548335797Z","updated_at":"2026-11-02T15:47:03.11707Z"}]}}