diff --git a/go.mod b/go.mod
index 10c2a90386bf9..b73e663ac62b5 100644
--- a/go.mod
+++ b/go.mod
@@ -76,7 +76,7 @@ require (
 	github.com/mattn/go-sqlite3 v1.14.16
 	github.com/meilisearch/meilisearch-go v0.24.0
 	github.com/mholt/archiver/v3 v3.5.1
-	github.com/microcosm-cc/bluemonday v1.0.24
+	github.com/microcosm-cc/bluemonday v1.0.25
 	github.com/minio/minio-go/v7 v7.0.52
 	github.com/minio/sha256-simd v1.0.0
 	github.com/msteinert/pam v1.1.0
diff --git a/go.sum b/go.sum
index 5949c283ea2c9..454214ea9db5f 100644
--- a/go.sum
+++ b/go.sum
@@ -877,8 +877,8 @@ github.com/mholt/acmez v1.1.0 h1:IQ9CGHKOHokorxnffsqDvmmE30mDenO1lptYZ1AYkHY=
 github.com/mholt/acmez v1.1.0/go.mod h1:zwo5+fbLLTowAX8o8ETfQzbDtwGEXnPhkmGdKIP+bgs=
 github.com/mholt/archiver/v3 v3.5.1 h1:rDjOBX9JSF5BvoJGvjqK479aL70qh9DIpZCl+k7Clwo=
 github.com/mholt/archiver/v3 v3.5.1/go.mod h1:e3dqJ7H78uzsRSEACH1joayhuSyhnonssnDhppzS1L4=
-github.com/microcosm-cc/bluemonday v1.0.24 h1:NGQoPtwGVcbGkKfvyYk1yRqknzBuoMiUrO6R7uFTPlw=
-github.com/microcosm-cc/bluemonday v1.0.24/go.mod h1:ArQySAMps0790cHSkdPEJ7bGkF2VePWH773hsJNSHf8=
+github.com/microcosm-cc/bluemonday v1.0.25 h1:4NEwSfiJ+Wva0VxN5B8OwMicaJvD8r9tlJWm9rtloEg=
+github.com/microcosm-cc/bluemonday v1.0.25/go.mod h1:ZIOjCQp1OrzBBPIJmfX4qDYFuhU02nx4bn030ixfHLE=
 github.com/miekg/dns v1.0.14/go.mod h1:W1PPwlIAgtquWBMBEV9nkV9Cazfe8ScdGz/Lj7v3Nrg=
 github.com/miekg/dns v1.1.54 h1:5jon9mWcb0sFJGpnI99tOMhCPyJ+RPVz5b63MQG0VWI=
 github.com/miekg/dns v1.1.54/go.mod h1:uInx36IzPl7FYnDcMeVWxj9byh7DutNykX4G9Sj60FY=
diff --git a/modules/markup/sanitizer.go b/modules/markup/sanitizer.go
index 59cde61a68167..9f97f1d5b13e0 100644
--- a/modules/markup/sanitizer.go
+++ b/modules/markup/sanitizer.go
@@ -6,6 +6,7 @@ package markup
 
 import (
 	"io"
+	"net/url"
 	"regexp"
 	"sync"
 
@@ -79,6 +80,14 @@ func createDefaultPolicy() *bluemonday.Policy {
 		policy.AllowURLSchemes(setting.Markdown.CustomURLSchemes...)
 	} else {
 		policy.AllowURLSchemesMatching(allowAllRegex)
+
+		// Even if every scheme is allowed, these three are blocked for security reasons
+		disallowScheme := func(*url.URL) bool {
+			return false
+		}
+		policy.AllowURLSchemeWithCustomPolicy("javascript", disallowScheme)
+		policy.AllowURLSchemeWithCustomPolicy("vbscript", disallowScheme)
+		policy.AllowURLSchemeWithCustomPolicy("data", disallowScheme)
 	}
 
 	// Allow classes for anchors
diff --git a/modules/markup/sanitizer_test.go b/modules/markup/sanitizer_test.go
index 0c22ce3ba0e78..4d85cbf9f303b 100644
--- a/modules/markup/sanitizer_test.go
+++ b/modules/markup/sanitizer_test.go
@@ -54,8 +54,13 @@ func Test_Sanitizer(t *testing.T) {
 		`<code style="bad-color: red">Hello World</code>`, `<code>Hello World</code>`,
 
 		// URLs
-		`[my custom URL scheme](cbthunderlink://somebase64string)`, `[my custom URL scheme](cbthunderlink://somebase64string)`,
-		`[my custom URL scheme](matrix:roomid/psumPMeAfzgAeQpXMG:feneas.org?action=join)`, `[my custom URL scheme](matrix:roomid/psumPMeAfzgAeQpXMG:feneas.org?action=join)`,
+		`<a href="cbthunderlink://somebase64string)">my custom URL scheme</a>`, `<a href="cbthunderlink://somebase64string)" rel="nofollow">my custom URL scheme</a>`,
+		`<a href="matrix:roomid/psumPMeAfzgAeQpXMG:feneas.org?action=join">my custom URL scheme</a>`, `<a href="matrix:roomid/psumPMeAfzgAeQpXMG:feneas.org?action=join" rel="nofollow">my custom URL scheme</a>`,
+
+		// Disallow dangerous url schemes
+		`<a href="javascript:alert('xss')">bad</a>`, `bad`,
+		`<a href="vbscript:no">bad</a>`, `bad`,
+		`<a href="data:1234">bad</a>`, `bad`,
 	}
 
 	for i := 0; i < len(testCases); i += 2 {