CVE-2026-25766: Echo has a Windows path traversal via backslash in middleware.Static default filesystem

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-02-19 · updated 2026-06-17
Weakness: CWE-22

Description

Echo is a Go web framework. In versions 5.0.0 through 5.0.2 on Windows, Echo’s `middleware.Static` using the default filesystem allows path traversal via backslashes, enabling unauthenticated remote file read outside the static root. In `middleware/static.go`, the requested path is unescaped and normalized with `path.Clean` (URL semantics). `path.Clean` does not treat `\` as a path separator, so `..\` sequences remain in the cleaned path. The resulting path is then passed to `currentFS.Open(...)`. When the filesystem is left at the default (nil), Echo uses `defaultFS` which calls `os.Open` (`echo.go:792`). On Windows, `os.Open` treats `\` as a path separator and resolves `..\`, allowing traversal outside the static root. Version 5.0.3 fixes the issue.

Affected products

labstack echo: from 5.0.0 before 5.0.3 — fixed in 5.0.3

How to fix

Upgrade to a fixed version: labstack echo 5.0.3. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-25766 or the next vulnerability affects your stack