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Fix open redirect vulnerability in OAuth return path #74

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Merged
ericmj merged 1 commit into from
Mar 10, 2026
Merged

Fix open redirect vulnerability in OAuth return path #74

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12 changes: 11 additions & 1 deletion lib/hexdocs/plug.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -97,7 +97,7 @@ defmodule Hexdocs.Plug do
conn
|> put_session("oauth_code_verifier", code_verifier)
|> put_session("oauth_state", state)
|> put_session("oauth_return_path", conn.request_path)
|> put_session("oauth_return_path", safe_return_path(conn.request_path))
|> redirect(url)
end

Expand Down Expand Up @@ -362,6 +362,16 @@ defmodule Hexdocs.Plug do
end)
end

defp safe_return_path("/" <> rest = path) do
if String.starts_with?(rest, "/") do
"/"
else
path
end
end

defp safe_return_path(_), do: "/"

defp redirect(conn, url) do
html = Plug.HTML.html_escape(url)
body = "<html><body>You are being <a href=\"#{html}\">redirected</a>.</body></html>"
Expand Down
18 changes: 18 additions & 0 deletions test/hexdocs/plug_test.exs
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,24 @@ defmodule Hexdocs.PlugTest do
assert get_session(conn, "oauth_return_path") == "/foo"
end

test "sanitize protocol-relative return path to prevent open redirect" do
conn = conn(:get, "http://plugtest.localhost:5002//evil.com") |> call()
assert conn.status == 302
assert get_session(conn, "oauth_return_path") == "/"
end

test "sanitize protocol-relative return path with extra slashes" do
conn = conn(:get, "http://plugtest.localhost:5002///evil.com/foo") |> call()
assert conn.status == 302
assert get_session(conn, "oauth_return_path") == "/"
end

test "preserve valid return path" do
conn = conn(:get, "http://plugtest.localhost:5002/some/path") |> call()
assert conn.status == 302
assert get_session(conn, "oauth_return_path") == "/some/path"
end

test "OAuth callback with invalid state returns error" do
conn =
conn(:get, "http://plugtest.localhost:5002/oauth/callback?code=abc&state=wrong")
Expand Down