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Vulnerabilities

Vulnerability · GHSA-r766-rf9f-588h

Host and :authority values with dot segments or slashes escape a {host}-based root

Published Nov 4, 2026 · catalog updated Nov 4, 2026 · Host and :authority values

Last checked Nov 4, 2026. A connected source was read within the last 7 days.

Open the advisory

Exploitation likelihood is not on this record for GHSA-r766-rf9f-588h. A missing EPSS score is not a low risk. Compare Host and :authority values with the linked advisory before you change production.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (Host and :authority values).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
  • EPSS is missing. A missing score is not a low risk.
Severity
High—
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
Awaiting synchronization with FIRST
Remediation
Version ranges on file
Affected products
go github.com/caddyserver/caddy/v2

### Summary A site whose root uses the request host ( ) lets the client choose the document root. HTTP/1.1 accepts , and the HTTP/2 and HTTP/3 servers accept and in , so moves the root anywhere on the filesystem. serves files and runs files outside the intended tree. ### Details What reaches Caddy, per protocol (Go 1.27, quic-go v0.63.0): | Host value | HTTP/1.1 ( or absolute-form) | HTTP/2 | HTTP/3 | |---|---|---|---| | , , | accepted | accepted | accepted | | contains , or a space | 400 | accepted | accepted | | contains NUL | 400 | stream error | stream error | covers only HTTP/1. The HTTP/2 and HTTP/3 servers check with alone, which rejects control bytes but allows , and spaces. The expanded root then goes through , which cleans the dot segments instead of rejecting them. On Windows, calls , which also trims trailing dots and spaces from the last segment, so can resolve like and like . Fix: applies to every protocol, and responds 400 when the host, port stripped, is made only of dots. Hosts such as keep working. Patch: public PR from . Discovered by Anthropic's OSS Scanner, as vulnerability ANT-2026-YKIEF8GR. ### Proof of concept Both return 200 on master. The same works over TLS with HTTP/2 and HTTP/3. ### Impact On catch-all or on-demand TLS sites with a host-derived root, unauthenticated clients read any file the Caddy process can read and, with or FrankenPHP, run any file on the filesystem. Sites that list their host names are not affected.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • go github.com/caddyserver/caddy/v2<= 2.11.7

How to fix GHSA-r766-rf9f-588h

  • Upgrade

    GHSA-r766-rf9f-588h lists a fix boundary at 2.11.7. Compare the installed build with that boundary before you change production.

  • Version check

    Affected <= 2.11.7

  • Advisory

    Open the inventory_github record and follow its fix.

  • Official advisories

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

Exploitation likelihood is not on this record for GHSA-r766-rf9f-588h. A missing EPSS score is not a low risk. Compare Host and :authority values with the linked advisory before you change production.

Which versions are affected?

Compare what you have installed with <= 2.11.7. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-22: Path Traversal. EPSS is not on this record yet. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Nov 4, 2026 · Maintainer security tabs

    Detected

    ### Summary A site whose root uses the request host ( ) lets the client choose the document root. HTTP/1.1 accepts , and the HTTP/2 and HTTP/3 servers accept and in , so moves the root anywhere on the filesystem. serves files and runs files outside the intended tree. ### Details What reaches Caddy, per protocol (Go 1.27, quic-go v0.63.0): | Host value | HTTP/1.1 ( or absolute-form) | HTTP/2 | HTTP

  2. Nov 4, 2026 · Maintainer security tabs

    Updated

    ### Summary A site whose root uses the request host ( ) lets the client choose the document root. HTTP/1.1 accepts , and the HTTP/2 and HTTP/3 servers accept and in , so moves the root anywhere on the filesystem. serves files and runs files outside the intended tree. ### Details What reaches Caddy, per protocol (Go 1.27, quic-go v0.63.0): | Host value | HTTP/1.1 ( or absolute-form) | HTTP/2 | HTTP

Sources

  • Maintainer security tabsVendor advisoryGHSA-r766-rf9f-588h

    ### Summary A site whose root uses the request host ( ) lets the client choose the document root. HTTP/1.1 accepts , and the HTTP/2 and HTTP/3 servers accept and in , so moves the root anywhere on the filesystem. serves files and runs files outside the intended tree. ### Details What reaches Caddy, per protocol (Go 1.27, quic-go v0.63.0): | Host value | HTTP/1.1 ( or absolute-form) | HTTP/2 | HTTP

    github.com

Freshness

Last verified in this catalog Nov 4, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • Maintainer security tabsNov 4, 2026