CVE-2026-25766: Github.com/labstack/echo/v5 Path Traversal Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-pgvm-wxw2-hrv9",
  "modified" : "2026-02-27T22:07:05Z",
  "published" : "2026-02-17T18:53:58Z",
  "aliases" : [ "CVE-2026-25766" ],
  "summary" : "Echo has a Windows path traversal via backslash in middleware.Static default filesystem",
  "details" : "### Summary\nOn Windows, Echo’s `middleware.Static` using the default filesystem allows path traversal via backslashes, enabling\nunauthenticated remote file read outside the static root.\n\n### Details  \n\n  In `middleware/static.go`, the requested path is unescaped and normalized with `path.Clean` (URL semantics).\n  `path.Clean` does **not** treat `\\` as a path separator, so `..\\` sequences remain in the cleaned path. The resulting\n  path is then passed to `currentFS.Open(...)`. When the filesystem is left at the default (nil), Echo uses `defaultFS`\n  which calls `os.Open` (`echo.go:792`). On Windows, `os.Open` treats `\\` as a path separator and resolves `..\\`,\n  allowing traversal outside the static root.\n\n  Relevant code:\n  - `middleware/static.go` (path unescape + `path.Clean` + `currentFS.Open`)\n  - `echo.go` `defaultFS.Open` → `os.Open`\n\n  This is the same class as CVE-2020-36565 (fixed in v4 by switching to OS-aware cleaning), but in v5 the `path.Clean`\n  + defaultFS combination reintroduces the Windows backslash traversal.\n\n\n### PoC\n Windows only.\n\n  **Sample code (main.go):**\n  ```go\n  package main\n\n  import (\n        \"log\"\n        \"net/http\"\n\n        \"github.com/labstack/echo/v5\"\n        \"github.com/labstack/echo/v5/middleware\"\n  )\n\n  func main() {\n        e := echo.New()\n\n        // Important: use middleware.Static with default filesystem (nil)\n        e.Use(middleware.Static(\"public\"))\n\n        e.GET(\"/healthz\", func(c *echo.Context) error {\n                return c.String(http.StatusOK, \"ok\")\n        })\n\n        addr := \":1323\"\n        log.Printf(\"listening on %s\", addr)\n        if err := e.Start(addr); err != nil && err != http.ErrServerClosed {\n                log.Fatal(err)\n        }\n  }\n ```\n  Static file:\n\n  public/index.html\n\n  (content can be any HTML)\n\n  **Run:**\n  go run .\n\n  **Verify:**\n\n  curl http://localhost:1323/index.html\n  curl --path-as-is \"http://localhost:1323/..%5c..%5cWindows%5cSystem32%5cdrivers%5cetc%5chosts\"\n  Expected: 404  \n\n  **Screenshot:**\n<img width=\"884\" height=\"689\" alt=\"image\" src=\"https://github.com/user-attachments/assets/acb14d70-2a43-47c1-8927-2f3da491a853\" />\n<img width=\"1022\" height=\"162\" alt=\"image\" src=\"https://github.com/user-attachments/assets/f2b92aa2-541e-461d-81a2-8a5907d7a447\" />\n\n\n\n  ### Impact\n  Path traversal leading to arbitrary file read outside the static root. Any unauthenticated remote user can\n  read local files that the Echo process has access to on Windows, if `middleware.Static` is used with the default\n  filesystem.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/labstack/echo/v5"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "5.0.0"
      }, {
        "fixed" : "5.0.3"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/labstack/echo/security/advisories/GHSA-pgvm-wxw2-hrv9"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-25766"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/labstack/echo/pull/2891"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/labstack/echo/commit/b1d443086ea27cf51345ec72a71e9b7e9d9ce5f1"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/labstack/echo"
  }, {
    "type" : "WEB",
    "url" : "https://pkg.go.dev/vuln/GO-2026-4502"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-17T18:53:58Z",
    "nvd_published_at" : "2026-02-19T16:27:15Z"
  }
}