From efe9d0a5f8097fb40d440d9f4013801b49d93b9e Mon Sep 17 00:00:00 2001
From: Joram Wilander <jwawilander@gmail.com>
Date: Tue, 7 May 2019 09:14:35 -0400
Subject: [PATCH] Fix panic in markdown link parsing (#10785)

---
 utils/markdown/autolink.go      |  4 ++++
 utils/markdown/autolink_test.go | 12 ++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/utils/markdown/autolink.go b/utils/markdown/autolink.go
index 7f7d1117f1..d362151aa7 100644
--- a/utils/markdown/autolink.go
+++ b/utils/markdown/autolink.go
@@ -78,6 +78,10 @@ func parseURLAutolink(data string, position int) (Range, bool) {
 		start -= 1
 	}
 
+	if start < 0 || position >= len(data) {
+		return Range{}, false
+	}
+
 	// Ensure that the URL scheme is allowed and that at least one character after the scheme is valid.
 	scheme := data[start:position]
 	if !isSchemeAllowed(scheme) || !isValidHostCharacter(data[position+3:]) {
diff --git a/utils/markdown/autolink_test.go b/utils/markdown/autolink_test.go
index 997124338a..c0e07f327b 100644
--- a/utils/markdown/autolink_test.go
+++ b/utils/markdown/autolink_test.go
@@ -130,6 +130,18 @@ func TestParseURLAutolink(t *testing.T) {
 			Position:    14,
 			Expected:    "http://example.com",
 		},
+		{
+			Description: "bad link protocol",
+			Input:       "://///",
+			Position:    0,
+			Expected:    "",
+		},
+		{
+			Description: "position greater than input length",
+			Input:       "there is no colon",
+			Position:    1000,
+			Expected:    "",
+		},
 	}
 
 	for _, testCase := range testCases {