Caddy: Windows file_server path authorization bypass via encoded backslash

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-52844: 0.62% estimated exploitation activity in the next 30 days; percentile 49.73 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary On Windows, Caddy path matchers treat /private\secret.txt as outside /private/, but fileserver later resolves the same request path as private\secret.txt on disk. An unauthenticated remote client can request /private%5csecret.txt and bypass Caddy path-scoped auth/deny routes protecting /private/. Details The mismatch is between two Caddy code paths: - MatchPath.MatchWithError() compares r.URL.Path using URL path semantics and does not normalize \ to /: modules/caddyhttp/matchers.go:429, :436, :490, :532. - If the route matcher misses, Caddy skips that route: modules/caddyhttp/routes.go:271. - fileserver then maps the same request path to a filesystem path with SanitizedPathJoin(root, r.URL.Path): modules/caddyhttp/fileserver/staticfiles.go:294, modules/caddyhttp/caddyhttp.go:257, :263. - On Windows, Go filesystem path handling treats \ as a separator, so the default filesystem opens the file under the protected directory: internal/filesystems/os.go:18. This is related to, but…

Published by the source

16 Jun 2026, 21:28 UTC

Last modified by the source

20 Jul 2026, 21:02 UTC

Source last checked

26 Oct 2026, 15:25 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-qrp7-cvwr-j2c6

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# Patch Next advisory brief: CVE-2026-52844

Advisory: Caddy: Windows `file_server` path authorization bypass via encoded backslash
IDs: CVE-2026-52844, GHSA-qrp7-cvwr-j2c6
Record: https://patchnext.com/advisories/cve-2026-52844 (revision 1, source checked 26 Oct 2026, 15:25 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: github.com/caddyserver/caddy/v2 2.11.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/caddyserver/caddy/v2: affected < 2.11.4; fixed in 2.11.4
- Go github.com/caddyserver/caddy: affected <= 1.0.5

## Suggested inspection (read-only)
- Go github.com/caddyserver/caddy/v2: check the installed version with your package manager.
- Go github.com/caddyserver/caddy: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/caddyserver/caddy/v2, github.com/caddyserver/caddy.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-qrp7-cvwr-j2c6 (GitHub-reviewed advisory GHSA-qrp7-cvwr-j2c6 lists affected ranges: Go github.com/caddyserver/caddy/v2 >=0 =0 <=1.0.5)

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