GHSA-HJR9-WJ7V-7HV8

Vulnerability from github – Published: 2026-01-05 19:43 – Updated: 2026-01-05 19:43
VLAI
Summary
Sliver Vulnerable to Pre-Auth Memory Exhaustion via NoEncoder Bypass
Details

Summary

A specially crafted nonce routes unauthenticated requests through the NoEncoder path, where startSessionHandler() reads the entire request body without limits, allowing attacker-driven memory exhaustion and process crash.

Details

  • server/encoders/encoders.go: EncoderFromNonce() returns NoEncoder when nonce % 65537 == 0 (lines 254-264); NoEncoder is a passthrough (util/encoders/nop.go:22-32).
  • server/c2/http.go: anonymousHandler() routes requests with any encoder (including NoEncoder) to startSessionHandler() (lines 551-562).
  • server/c2/http.go: startSessionHandler() uses io.ReadAll(req.Body) without a size cap (lines 564-643), unlike the authenticated path that uses io.LimitedReader (readReqBody(), lines 708-732).

PoC

An attacker could send an HTTP POST with a nonce that is a multiple of 65537 (e.g., ?q=65537) so it is handled by startSessionHandler() with a NoEncoder, and advertise a very large Content-Length while streaming data. Because this handler uses io.ReadAll(req.Body) without a size limit, the server is expected to allocate large amounts of memory and may exhaust available RAM, leading to process termination on typical deployments.

Impact

Unauthenticated remote DoS: attacker can crash the Sliver HTTP listener, dropping all active sessions and locking out operators until restart. No credentials or non-default config required.

Severity
5.5 (Medium)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/bishopfox/sliver"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.5.0"
            },
            {
              "last_affected": "1.5.44"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-01-05T19:43:06Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\nA specially crafted nonce routes unauthenticated requests through the NoEncoder path, where `startSessionHandler()` reads the entire request body without limits, allowing attacker-driven memory exhaustion and process crash.\n\n### Details\n- `server/encoders/encoders.go`: `EncoderFromNonce()` returns NoEncoder when `nonce % 65537 == 0` (lines 254-264); NoEncoder is a passthrough (`util/encoders/nop.go:22-32`).\n- `server/c2/http.go`: `anonymousHandler()` routes requests with any encoder (including NoEncoder) to `startSessionHandler()` (lines 551-562).\n- `server/c2/http.go`: `startSessionHandler()` uses `io.ReadAll(req.Body)` without a size cap (lines 564-643), unlike the authenticated path that uses `io.LimitedReader` (`readReqBody()`, lines 708-732).\n\n### PoC\nAn attacker could send an HTTP POST with a nonce that is a multiple of 65537 (e.g., ?q=65537) so it is handled by startSessionHandler() with a NoEncoder, and advertise a very large Content-Length while streaming data. Because this handler uses io.ReadAll(req.Body) without a size limit, the server is expected to allocate large amounts of memory and may exhaust available RAM, leading to process termination on typical deployments.\n\n### Impact\nUnauthenticated remote DoS: attacker can crash the Sliver HTTP listener, dropping all active sessions and locking out operators until restart. No credentials or non-default config required.",
  "id": "GHSA-hjr9-wj7v-7hv8",
  "modified": "2026-01-05T19:43:06Z",
  "published": "2026-01-05T19:43:06Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/BishopFox/sliver/security/advisories/GHSA-hjr9-wj7v-7hv8"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/BishopFox/sliver"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Sliver Vulnerable to Pre-Auth Memory Exhaustion via NoEncoder Bypass"
}



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