Complaint: Karlsruhe temporarily halts controversial DNS surveillance

The Federal Constitutional Court has halted the execution of a controversial judicial order that would have obliged a telecommunications provider to mass-monitor requests via the Domain Name System (DNS) (File No. 1 BvR 2317/25). The Karlsruhe judges have temporarily suspended a corresponding order from the Oldenburg District Court dated November 5, 2025, and prohibited further orders.

Two group subsidiaries of a major telecommunications provider had filed constitutional complaints against decisions by the Oldenburg District and Regional Courts. The decisions obliged network operators to "monitor and record domestic Domain Name System requests" to a specific server.

It is not known what kind of server this is or in which direction the investigations are heading. The network operators also did not gain insight into the prosecution's investigation file upon request. The surveillance orders are based on Section 100a of the Code of Criminal Procedure (StPO), which regulates the tapping of classic telephone calls or access to emails based on a catalog of offenses that has been continuously expanded over the years.

The affected network operators argued that the order was novel and required considerable organizational and personnel effort. They would have to evaluate all DNS server requests from approximately 40 million customers. The number of affected DNS requests was estimated to be around 5 million per second.

Careful Impact Assessment

The Federal Constitutional Court suspended the order from Oldenburg by way of its own interim order in a decision published on November 25. This is possible if the balancing of the threatened consequences, with an open outcome of the main proceedings, so dictates.

The chamber found that the constitutional complaint was "neither inadmissible nor obviously unfounded after a summary examination at the current stage of proceedings." The balancing of consequences therefore favored the companies. The Karlsruhe judges justified this, for example, with regard to the consequences of a later success of the complaint: the providers would first have to implement the measure, which was ultimately found to be unconstitutional, with considerable effort. They also faced irreversible reputational damage.

According to the Federal Constitutional Court, the threatened mass and irreversible infringements on customers' telecommunications secrecy weigh particularly heavily. The Karlsruhe judges emphasize that many affected individuals were subjected to surveillance without their own suspicion of a crime and, due to the secrecy of the measure, had no preventive or defensive legal protection.

Ultimately, the chamber saw no particularly high interest in prosecution that would have argued against suspending the measure. The disadvantages for the complainants and the threatened mass infringements on the fundamental rights of customers clearly outweighed this. The suspension is in effect for a maximum of six months for the time being. A decision in the main proceedings should have been made by then.

The Constitutional Court does not name the affected provider. However, the stated number of 40 million customers points to one of the major German network operators. On inquiry from heise online, the lawyers at Telekom shrugged their shoulders with the sentiment: No knowledge. The matter was also initially unknown at Telefónica Deutschland, according to company circles.

"Legal Milestone"

According to IT lawyer Jens Ferner, the decision is a "legal milestone" of fundamental importance. It touches upon the foundations of telecommunications secrecy and marks an important boundary for the digital investigation methods of state authorities. The lawyer emphasizes that investigative authorities are naturally interested in using digital traces and thereby "pushing boundaries a little further."

Ferner sees DNS monitoring as an attempt to establish unwarranted mass surveillance similar to data retention. The goal is to intercept specific IP addresses that access or are interested in a particular website, Ferner writes. DNS requests, which are a "central component of internet use," are often not even directly linked to accessing a website. This would also affect the "technical infrastructure of the internet."

(vbr)