{"id":"GHSA-g7r4-m6w7-qqqr","revision":null,"records":[{"revision":"cf89a814906b49a5ade144ad898cf4e9","observedAt":"2026-10-24T13:17:17.793+00:00","statement":{"source":"osv","id":"GHSA-g7r4-m6w7-qqqr","aliases":[],"title":"esbuild allows arbitrary file read when running the development server on Windows","description":"### Summary\n\nThe development server contains a path traversal vulnerability on Windows when serving files from `servedir`.\n\nDue to the use of `path.Clean()` (which only normalizes forward-slash `/` separators) instead of a Windows-aware path normalization function, it is possible to craft requests using backslashes (`\\`) that bypass the intended directory containment logic. An attacker can escape the configured `servedir` root and access arbitrary files on the filesystem.\nThis issue affects Windows environments only.\n\n### Details\n\nThe request path is sanitized using:\n```go\n// https://github.com/evanw/esbuild/blob/v0.27.3/pkg/api/serve_other.go#L165\nqueryPath := path.Clean(req.URL.Path)[1:]\n```\n\n\nHowever:\n- `path.Clean()` is POSIX-style and only understands `/` (docs: `https://pkg.go.dev/path#Clean`)\n- On Windows, `\\` is a valid path separator\n- `path.Clean()` does not treat `\\` as a separator\n\nLater, the server constructs the absolute path:\n```go\n// https://github.com/evanw/esbuild/blob/v0.27.3/pkg/api/serve_other.go#L221\nabsPath := h.fs.Join(h.servedir, queryPath)\n```\n\nIf `queryPath` contains sequences such as:\n```\n..\\..\\..\\..\\..\\..\\..\\Windows\\system.ini\n```\n\n`path.Clean()` will not normalize them, but the Windows filesystem will interpret `\\` as directory separators when resolving `absPath`.\nBecause the implementation does not verify that the final resolved path remains within `servedir`, it allows directory traversal outside the intended root directory.\n### Vulnerable Code\n\n```go\n// https://github.com/evanw/esbuild/blob/v0.27.3/pkg/api/serve_other.go#L165\n\tqueryPath := path.Clean(req.URL.Path)[1:]\n\t....\n\t// Check for a file in the \"servedir\" directory\n\tif h.servedir != \"\" && kind != fs.FileEntry {\n\t\tabsPath := h.fs.Join(h.servedir, queryPath)\n\t\tif absDir := h.fs.Dir(absPath); absDir != absPath {\n\t\t\tif entries, err, _ := h.fs.ReadDirectory(absDir); err == nil {\n\t\t\t\tif entry, _ := entries.Get(h.fs.Base(absPath)); entry != nil && entry.Kind(h.fs) == fs.FileEntry {\n\t....\t\t\t\t\n```\n\n\n### Steps to reproduce\n\n```\nnpm install --save-exact --save-dev esbuild\n\necho \"console.log(1)\" > app.js\n\n.\\node_modules\\.bin\\esbuild --version\n0.27.3\n\n.\\node_modules\\.bin\\esbuild app.js --bundle --outdir=www --servedir=www --watch\n\ncurl -i --path-as-is \"http://localhost:8000/..\\..\\..\\..\\..\\..\\..\\Windows\\system.ini\"\n<content of Windows\\system.ini>\n```\n\n\n### Impact\n\n- Arbitrary file read on Windows\n- Exposure of sensitive files","state":0,"publishedAt":"2026-06-12T20:08:53+00:00","modifiedAt":"2026-09-10T03:50:49.4276923+00:00","affected":[{"ecosystem":"npm","name":"esbuild","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0.27.3"},{"kind":"fixed","version":"0.28.1"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V3","vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"LOW"}],"references":["https://github.com/evanw/esbuild/security/advisories/GHSA-g7r4-m6w7-qqqr","https://github.com/evanw/esbuild","https://github.com/evanw/esbuild/releases/tag/v0.28.1"],"sourceUrl":"https://github.com/advisories/GHSA-g7r4-m6w7-qqqr","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-g7r4-m6w7-qqqr","identifiers":["GHSA-g7r4-m6w7-qqqr"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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