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CVE-2026-39418

Status: AnalyzedHigh (7.4)—

MaxKB is an open-source AI assistant for enterprise. In versions 2.7.1 and below, sandbox network protection can be bypassed by using socket.sendto() with the MSG_FASTOPEN flag. This allows authenticated user with tool-editing permissions to reach internal services that are explicitly blocked by the sandbox's banned hosts configuration.

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MaxKB's sandbox uses LD_PRELOAD to hook the connect() function and block connections to banned IPs, but Linux's sendto() with the MSG_FASTOPEN flag can establish TCP connections directly through the kernel without ever calling connect(), completely bypassing the IP validation. Although sendto is listed in the syscall() wrapper, this is ineffective because glibc invokes the kernel syscall directly rather than routing through the hooked syscall() function. This issue has been fixed in version 2.8.0.

CVSS

Exploitation probability (EPSS)

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

🎯 ATT&CK techniques

How this vulnerability is exploited and what the attacker gains, in MITRE ATT&CK terms.

Vulnerabilidad de bypass de sandbox en MaxKB que permite a usuario autenticado (PR:L) alcanzar servicios internos bloqueados (CWE-918: SSRF). El bypass del LD_PRELOAD mediante sendto() con MSG_FASTOPEN (acceso a red interna) y potencial lectura de datos de servicios internos.

Inferred by our analysis agent from the official description, CVSS vector and CWE, and checked by a supervisor. May contain errors.

🛡️ ATT&CK mitigations that cover these techniques

Vulnerability ScanningThreat Intelligence ProgramSSL/TLS InspectionPrivileged Account ManagementNetwork SegmentationNetwork Intrusion Prevention

Affected technologies (1)

Maxkb — Maxkb

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2026-39418",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-39418",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-04-14T15:54:18.732139Z"
        }
      }
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    "cvssMetricV31": [
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        "type": "Secondary",
        "source": "security-advisories@github.com",
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          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 5,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L",
          "integrityImpact": "LOW",
          "userInteraction": "NONE",
          "attackComplexity": "HIGH",
          "availabilityImpact": "LOW",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "LOW"
        },
        "impactScore": 3.4,
        "exploitabilityScore": 1.6
      },
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
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          "attackVector": "NETWORK",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:L",
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  "affected": [
    {
      "source": "security-advisories@github.com",
      "affectedData": [
        {
          "vendor": "1Panel-dev",
          "product": "MaxKB",
          "versions": [
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              "status": "affected",
              "version": "< 2.8.0"
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  "published": "2026-04-14T01:16:04.353",
  "references": [
    {
      "url": "https://github.com/1Panel-dev/MaxKB/commit/4d06362750b15390437f1d2e4d14ec79baef8559",
      "tags": [
        "Patch"
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      "source": "security-advisories@github.com"
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    {
      "url": "https://github.com/1Panel-dev/MaxKB/releases/tag/v2.8.0",
      "tags": [
        "Release Notes"
      ],
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/1Panel-dev/MaxKB/security/advisories/GHSA-w9g4-q3gm-6q6w",
      "tags": [
        "Vendor Advisory"
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "security-advisories@github.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-918"
        }
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  "descriptions": [
    {
      "lang": "en",
      "value": "MaxKB is an open-source AI assistant for enterprise. In versions 2.7.1 and below, sandbox network protection can be bypassed by using socket.sendto() with the MSG_FASTOPEN flag. This allows authenticated user with tool-editing permissions to reach internal services that are explicitly blocked by the sandbox's banned hosts configuration. MaxKB's sandbox uses LD_PRELOAD to hook the connect() function and block connections to banned IPs, but Linux's sendto() with the MSG_FASTOPEN flag can establish TCP connections directly through the kernel without ever calling connect(), completely bypassing the IP validation. Although sendto is listed in the syscall() wrapper, this is ineffective because glibc invokes the kernel syscall directly rather than routing through the hooked syscall() function. This issue has been fixed in version 2.8.0."
    }
  ],
  "lastModified": "2026-06-17T10:42:05.177",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:maxkb:maxkb:*:*:*:*:-:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "8BB376B6-4E9C-4801-9D33-5BF858C857D2",
              "versionEndExcluding": "2.8.0"
            }
          ],
          "operator": "OR"
        }
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  "sourceIdentifier": "security-advisories@github.com"
}