Only match credential entries with correct namespace in the Windows Credential Manager

src/shared/Core.Tests/Interop/Windows/WindowsCredentialManagerTests.cs

@@ -270,6 +270,70 @@ public void WindowsCredentialManager_IsMatch(
             Assert.Equal(expected, actual);
         }
 
+        [PlatformFact(Platforms.Windows)]
+        public void WindowsCredentialManager_IsMatch_NoNamespace_NotMatched()
+        {
+            var win32Cred = new Win32Credential
+            {
+                UserName = "test",
+                TargetName = $"{WindowsCredentialManager.TargetNameLegacyGenericPrefix}https://example.com"
+            };
+
+            var credManager = new WindowsCredentialManager(TestNamespace);
+
+            bool result = credManager.IsMatch("https://example.com", null, win32Cred);
+
+            Assert.False(result);
+        }
+
+        [PlatformFact(Platforms.Windows)]
+        public void WindowsCredentialManager_IsMatch_DifferentNamespace_NotMatched()
+        {
+            var win32Cred = new Win32Credential
+            {
+                UserName = "test",
+                TargetName = $"{WindowsCredentialManager.TargetNameLegacyGenericPrefix}:random-namespace:https://example.com"
+            };
+
+            var credManager = new WindowsCredentialManager(TestNamespace);
+
+            bool result = credManager.IsMatch("https://example.com", null, win32Cred);
+
+            Assert.False(result);
+        }
+
+        [PlatformFact(Platforms.Windows)]
+        public void WindowsCredentialManager_IsMatch_CaseSensitiveNamespace_NotMatched()
+        {
+            var win32Cred = new Win32Credential
+            {
+                UserName = "test",
+                TargetName = $"{WindowsCredentialManager.TargetNameLegacyGenericPrefix}:nAmEsPaCe:https://example.com"
+            };
+
+            var credManager = new WindowsCredentialManager("namespace");
+
+            bool result = credManager.IsMatch("https://example.com", null, win32Cred);
+
+            Assert.False(result);
+        }
+
+        [PlatformFact(Platforms.Windows)]
+        public void WindowsCredentialManager_IsMatch_NoNamespaceInQuery_IsMatched()
+        {
+            var win32Cred = new Win32Credential
+            {
+                UserName = "test",
+                TargetName = $"{WindowsCredentialManager.TargetNameLegacyGenericPrefix}https://example.com"
+            };
+
+            var credManager = new WindowsCredentialManager();
+
+            bool result = credManager.IsMatch("https://example.com", null, win32Cred);
+
+            Assert.True(result);
+        }
+
         [PlatformTheory(Platforms.Windows)]
         [InlineData("https://example.com", null, "https://example.com")]
         [InlineData("https://example.com", "bob", "https://[email protected]")]

src/shared/Core/Interop/Windows/WindowsCredentialManager.cs

@@ -274,11 +274,19 @@ private WindowsCredential CreateCredentialFromStructure(Win32Credential credenti
                 return false;
             }
 
-            // Trim the "LegacyGeneric" prefix Windows adds and any namespace we have been filtered with
+            // Trim the "LegacyGeneric" prefix Windows adds
             string targetName = credential.TargetName.TrimUntilIndexOf(TargetNameLegacyGenericPrefix);
+
+            // Only match credentials with the namespace we have been configured with (if any)
             if (!string.IsNullOrWhiteSpace(_namespace))
             {
-                targetName = targetName.TrimUntilIndexOf($"{_namespace}:");
+                string nsPrefix = $"{_namespace}:";
+                if (!targetName.StartsWith(nsPrefix, StringComparison.Ordinal))
+                {
+                    return false;
+                }
+
+                targetName = targetName.Substring(nsPrefix.Length);
             }
 
             // If the target name matches the service name exactly then return 'match'