CVE-2026-52844: Caddy: Windows `file_server` path authorization bypass via encoded backslash

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-06-23 · updated 2026-10-25
Weakness: CWE-22

Description

Caddy is an extensible server platform that uses TLS by default. Prior to 2.11.4, on Windows, Caddy path matchers treat /private\secret.txt as outside /private/*, but file_server later resolves the same request path as private\secret.txt on disk. An unauthenticated remote client can bypass Caddy path-scoped auth/deny routes protecting /private/*. This vulnerability is fixed in 2.11.4.

Affected products

caddyserver caddy: before 2.11.4 — fixed in 2.11.4

How to fix

Upgrade to a fixed version: caddyserver caddy 2.11.4. Check the vendor advisory for mitigations.

References

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