CVE-2026-32136: AdGuard Home: HTTP/2 Cleartext (h2c) Upgrade Authentication Bypass

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.8%, percentile 57: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 57% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes github.com/AdguardTeam/AdGuardHome (Go) < 0.107.73, fixed in 0.107.73. Check your lockfile, including transitive dependencies.

What it is

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.

From the GitHub advisory

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 }

Weakness type: CWE-287.

Product: github.com/AdguardTeam/AdGuardHome (Go) · Assigned by: GitHub_M · Published: 2026-03-11

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.81% probability of exploitation activity in the next 30 days; percentile 57.

Timeline

• 2026-03-11 — CVE record published by GitHub_M
• 2026-03-12 — CVE record last updated
• 2026-03-12 — GitHub-reviewed advisory GHSA-5fg6-wrq4-w5gh published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-5fg6-wrq4-w5gh github.com
2. CVE.org record CVE-2026-32136 cve.org
3. NVD entry CVE-2026-32136 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com

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