Caddy: Windows `file_server` path authorization bypass via encoded backslash

published 2026-06-16 4 mo ago modified 2026-10-25 14 d ago also GHSA-qrp7-cvwr-j2c6 , GO-2026-5595 , EUVD-2026-38557

cvss: 7.5; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.6%; EPSS 0.6% chance of exploitation in 30 days, percentile 49%
public exploits: 0; none known

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.

Patch / fix

fixed in 2 distros 2

go github.com/caddyserver/caddy/v2 2.11.4
caddyserver caddy 2.11.4

suse opensuse

govulncheck-vulndb SLES 16.0, SLES for SAP applications 16.0 0.0.20260727T201416-160000.1.1

suse advisories SUSE-SU-2026:23216-1 SUSE-SU-2026:23227-1

govulncheck-vulndb openSUSE Leap 16.0 0.0.20260727T201416-160000.1.1

opensuse advisories openSUSE-SU-2026:21551-1

CISA SSVC

Exploitation: Proof of concept is public
Automatable: yes
Technical impact: partial
Assessed: 4 mo ago (2026-06-23)

Exploit prediction

0.62% chance of exploitation in the next 30 days, higher than 49% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/caddyserver/caddy/security/advisories/GHSA-qrp7-cvwr-j2c6 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	3.1	7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
GitHub	3.1	7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem	package	affected	fixed in
go	github.com/caddyserver/caddy/v2	<2.11.4	2.11.4
go	github.com/caddyserver/caddy	<=1.0.5	no fix listed

Affected products

caddyserver caddy

Classification

Weakness

CWE-22 Improper Limitation of a Pathname to a Restricted Directory
CWE-284 Improper Access Control

References

github.com /caddyserver/caddy/security/advisories/GHSA-qrp7-cvwr-j2c6
exploit, web, third-party-advisory, advisory
nvd.nist.gov /vuln/detail/CVE-2026-52844
advisory
github.com /caddyserver/caddy
package

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary