vole
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A free and open-source forge that lives in your Git repo.
| 1 | package web |
| 2 | |
| 3 | import ( |
| 4 | "strings" |
| 5 | "testing" |
| 6 | |
| 7 | "golang.org/x/net/html" |
| 8 | ) |
| 9 | |
| 10 | // The attributes that carry a destination. A scheme the browser will run is a |
| 11 | // click away from being script in this origin, so these are what the sanitizer |
| 12 | // has to have rewritten or removed. |
| 13 | var urlAttrs = map[string]bool{ |
| 14 | "href": true, "src": true, "action": true, "formaction": true, |
| 15 | "poster": true, "data": true, "xlink:href": true, |
| 16 | } |
| 17 | |
| 18 | // The elements that stop being text. bluemonday's UGC policy should remove all of |
| 19 | // them; the test is here so that loosening the policy fails rather than ships. |
| 20 | var unsafeElems = map[string]bool{ |
| 21 | "script": true, "iframe": true, "object": true, "embed": true, |
| 22 | "form": true, "style": true, "link": true, "meta": true, "base": true, |
| 23 | } |
| 24 | |
| 25 | var safeSchemes = map[string]bool{"": true, "http": true, "https": true, "mailto": true} |
| 26 | |
| 27 | // FuzzRenderMarkdown drives the boundary where untrusted text becomes HTML: |
| 28 | // goldmark renders it and bluemonday sanitises it, and the result is trusted |
| 29 | // enough to put in a page. |
| 30 | // |
| 31 | // The assertions parse the output instead of searching the string, which is the |
| 32 | // difference that matters: `<script>` as text is a text node and harmless, while |
| 33 | // `<script>` written by hand looks the same to a substring search. Parsing |
| 34 | // asks what the browser will do. |
| 35 | // |
| 36 | // Both document shapes are checked: a body with no place in a tree (an issue or a |
| 37 | // comment), and a README whose relative links are rewritten on the way out. |
| 38 | func FuzzRenderMarkdown(f *testing.F) { |
| 39 | for _, seed := range []string{ |
| 40 | "plain text", |
| 41 | "<script>alert(1)</script>", |
| 42 | "<img src=x onerror=alert(1)>", |
| 43 | "<IMG SRC=x ONERROR=alert(1)>", |
| 44 | "[link](javascript:alert(1))", |
| 45 | "[link](JaVaScRiPt:alert(1))", |
| 46 | "[link](data:text/html,<script>alert(1)</script>)", |
| 47 | "<a href=\"jav	ascript:alert(1)\">x</a>", |
| 48 | "[link](vbscript:msgbox)", |
| 49 | "<!-- comment --><script>x</script>", |
| 50 | "```\n<script>alert(1)</script>\n```\n", |
| 51 | "<script>alert(1)</script>", |
| 52 | "<svg><script>alert(1)</script></svg>", |
| 53 | "<iframe src=\"https://example.invalid\"></iframe>", |
| 54 | "<style>body{background:url(javascript:alert(1))}</style>", |
| 55 | "| a | b |\n|---|---|\n| 1 | 2 |\n", |
| 56 | "[relative](docs/other.md#heading) and ", |
| 57 | "[climb](../../../../etc/passwd)", |
| 58 | "[abs](//example.invalid/x)", |
| 59 | "# heading\n\n- item\n\n> quote\n", |
| 60 | "", |
| 61 | } { |
| 62 | f.Add(seed) |
| 63 | } |
| 64 | f.Fuzz(func(t *testing.T, src string) { |
| 65 | w := &Web{} |
| 66 | for _, doc := range []treeDoc{ |
| 67 | {Repo: "demo"}, // an issue body: no tree |
| 68 | {Repo: "demo", Ref: "main", Path: "docs/x.md"}, // a README: links rewritten |
| 69 | } { |
| 70 | out := string(w.renderTreeMarkdown(doc, src)) |
| 71 | root, err := html.Parse(strings.NewReader(out)) |
| 72 | if err != nil { |
| 73 | t.Fatalf("rendered HTML does not parse: %v\n%s", err, out) |
| 74 | } |
| 75 | checkHTML(t, root, out, src) |
| 76 | } |
| 77 | }) |
| 78 | } |
| 79 | |
| 80 | func checkHTML(t *testing.T, n *html.Node, out, src string) { |
| 81 | t.Helper() |
| 82 | if n.Type == html.ElementNode { |
| 83 | name := strings.ToLower(n.Data) |
| 84 | if unsafeElems[name] { |
| 85 | t.Fatalf("%q rendered a <%s> element:\n%s", src, name, out) |
| 86 | } |
| 87 | for _, attr := range n.Attr { |
| 88 | key := strings.ToLower(attr.Key) |
| 89 | // An event handler is script that runs on an event, whatever the tag. |
| 90 | if strings.HasPrefix(key, "on") { |
| 91 | t.Fatalf("%q rendered a %s attribute:\n%s", src, attr.Key, out) |
| 92 | } |
| 93 | value := strings.ToLower(strings.TrimSpace(attr.Val)) |
| 94 | switch { |
| 95 | case urlAttrs[key]: |
| 96 | // A scheme is the part before the first colon, unless the colon is |
| 97 | // inside a path or query. Anything not on the list is a scheme a |
| 98 | // browser may act on. |
| 99 | if scheme, ok := urlScheme(value); ok && !safeSchemes[scheme] { |
| 100 | t.Fatalf("%q rendered %s=%q:\n%s", src, attr.Key, attr.Val, out) |
| 101 | } |
| 102 | case key == "srcset" || key == "style": |
| 103 | // These hold more than one value, so the check is for the schemes |
| 104 | // that matter rather than for a parse. |
| 105 | for _, bad := range []string{"javascript:", "vbscript:", "expression("} { |
| 106 | if strings.Contains(value, bad) { |
| 107 | t.Fatalf("%q rendered %s=%q:\n%s", src, attr.Key, attr.Val, out) |
| 108 | } |
| 109 | } |
| 110 | } |
| 111 | } |
| 112 | } |
| 113 | for child := n.FirstChild; child != nil; child = child.NextSibling { |
| 114 | checkHTML(t, child, out, src) |
| 115 | } |
| 116 | } |
| 117 | |
| 118 | // urlScheme reports the scheme of a link destination, and whether there is one. |
| 119 | func urlScheme(value string) (string, bool) { |
| 120 | value = strings.TrimLeft(value, " \t\r\n") |
| 121 | i := strings.IndexByte(value, ':') |
| 122 | if i <= 0 { |
| 123 | return "", false |
| 124 | } |
| 125 | scheme := value[:i] |
| 126 | for _, r := range scheme { |
| 127 | if !(r == '+' || r == '-' || r == '.' || (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9')) { |
| 128 | // A colon that is not part of a scheme is part of a path, e.g. "a:b.md". |
| 129 | return "", false |
| 130 | } |
| 131 | } |
| 132 | return scheme, scheme != "" |
| 133 | } |
| 134 |