CVE-2025-47950

CoreDNS is a DNS server that chains plugins. In versions prior to 1.12.2, a Denial of Service (DoS) vulnerability exists in the CoreDNS DNS-over-QUIC (DoQ) server implementation. The server previously created a new goroutine for every incoming QUIC stream without imposing any limits on the number of concurrent streams or goroutines. A remote, unauthenticated attacker could open a large number of streams, leading to uncontrolled memory consumption and eventually causing an Out Of Memory (OOM) crash — especially in containerized or memory-constrained environments. The patch in version 1.12.2 introduces two key mitigation mechanisms: max_streams, which caps the number of concurrent QUIC streams per connection with a default value of 256; and worker_pool_size, which Introduces a server-wide, bounded worker pool to process incoming streams with a default value of 1024. This eliminates the 1:1 stream-to-goroutine model and ensures that CoreDNS remains resilient under high concurrency. Some workarounds are available for those who are unable to upgrade. Disable QUIC support by removing or commenting out the quic:// block in the Corefile, use container runtime resource limits to detect and isolate excessive memory usage, and/or monitor QUIC connection patterns and alert on anomalies.

CoreDNS is a DNS server that chains plugins. In versions prior to 1.12.2, a Denial of Service (DoS) vulnerability exists in the CoreDNS DNS-over-QUIC (DoQ) server implementation. The server previously created a new goroutine for every incoming QUIC stream without imposing any limits on the number of concurrent streams or goroutines. A remote, unauthenticated attacker could open a large number of streams, leading to uncontrolled memory consumption and eventually causing an Out Of Memory (OOM) crash — especially in containerized or memory-constrained environments. The patch in version 1.12.2 introduces two key mitigation mechanisms: max_streams, which caps the number of concurrent QUIC streams per connection with a default value of 256; and worker_pool_size, which Introduces a server-wide, bounded worker pool to process incoming streams with a default value of 1024. This eliminates the 1:1 stream-to-goroutine model and ensures that CoreDNS remains resilient under high concurrency. Some workarounds are available for those who are unable to upgrade. Disable QUIC support by removing or commenting out the quic:// block in the Corefile, use container runtime resource limits to detect and isolate excessive memory usage, and/or monitor QUIC connection patterns and alert on anomalies.

Summary

A Denial of Service (DoS) vulnerability was discovered in the CoreDNS DNS-over-QUIC (DoQ) server implementation. The server previously created a new goroutine for every incoming QUIC stream without imposing any limits on the number of concurrent streams or goroutines. A remote, unauthenticated attacker could open a large number of streams, leading to uncontrolled memory consumption and eventually causing an Out Of Memory (OOM) crash — especially in containerized or memory-constrained environments.

Impact

• Component: server_quic.go
• Attack Vector: Remote, network-based
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Impact: High availability loss (OOM kill or unresponsiveness)

This issue affects deployments with quic:// enabled in the Corefile. A single attacker can cause the CoreDNS instance to become unresponsive using minimal bandwidth and CPU.

Patches

The patch introduces two key mitigation mechanisms:

• max_streams: Caps the number of concurrent QUIC streams per connection. Default: 256.
• worker_pool_size: Introduces a server-wide, bounded worker pool to process incoming streams. Default: 1024.

This eliminates the 1:1 stream-to-goroutine model and ensures that CoreDNS remains resilient under high concurrency. The new configuration options are exposed through the quic Corefile block:

quic {
    max_streams 256
    worker_pool_size 1024
}

These defaults are generous and aligned with typical DNS-over-QUIC client behavior.

Workarounds

If you're unable to upgrade immediately, you can:

• Disable QUIC support by removing or commenting out the quic:// block in your Corefile
• Use container runtime resource limits to detect and isolate excessive memory usage
• Monitor QUIC connection patterns and alert on anomalies

References

• RFC 9250 - DNS over Dedicated QUIC Connections
• quic-go GitHub project
• QUIC stream exhaustion class of vulnerabilities (related)

Credit

Thanks to @thevilledev for disclovering this vulnerability and contributing a high-quality fix.

For more information

Please consult our security guide for more information regarding our security process.

CoreDNS is a DNS server that chains plugins. In versions prior to 1.12.2, a Denial of Service (DoS) vulnerability exists in the CoreDNS DNS-over-QUIC (DoQ) server implementation. The server previously created a new goroutine for every incoming QUIC stream without imposing any limits on the number of concurrent streams or goroutines. A remote, unauthenticated attacker could open a large number of streams, leading to uncontrolled memory consumption and eventually causing an Out Of Memory (OOM) crash — especially in containerized or memory-constrained environments. The patch in version 1.12.2 introduces two key mitigation mechanisms: max_streams, which caps the number of concurrent QUIC streams per connection with a default value of 256; and worker_pool_size, which Introduces a server-wide, bounded worker pool to process incoming streams with a default value of 1024. This eliminates the 1:1 stream-to-goroutine model and ensures that CoreDNS remains resilient under high concurrency. Some workarounds are available for those who are unable to upgrade. Disable QUIC support by removing or commenting out the quic:// block in the Corefile, use container runtime resource limits to detect and isolate excessive memory usage, and/or monitor QUIC connection patterns and alert on anomalies.

CoreDNS is a DNS server that chains plugins. In versions prior to 1.12.2, a Denial of Service (DoS) vulnerability exists in the CoreDNS DNS-over-QUIC (DoQ) server implementation. The server previously created a new goroutine for every incoming QUIC stream without imposing any limits on the number of concurrent streams or goroutines. A remote, unauthenticated attacker could open a large number of streams, leading to uncontrolled memory consumption and eventually causing an Out Of Memory (OOM) crash — especially in containerized or memory-constrained environments. The patch in version 1.12.2 introduces two key mitigation mechanisms: max_streams, which caps the number of concurrent QUIC streams per connection with a default value of 256; and worker_pool_size, which Introduces a server-wide, bounded worker pool to process incoming streams with a default value of 1024. This eliminates the 1:1 stream-to-goroutine model and ensures that CoreDNS remains resilient under high concurrency. Some workarounds are available for those who are unable to upgrade. Disable QUIC support by removing or commenting out the quic:// block in the Corefile, use container runtime resource limits to detect and isolate excessive memory usage, and/or monitor QUIC connection patterns and alert on anomalies.

Summary

A Denial of Service (DoS) vulnerability was discovered in the CoreDNS DNS-over-QUIC (DoQ) server implementation. The server previously created a new goroutine for every incoming QUIC stream without imposing any limits on the number of concurrent streams or goroutines. A remote, unauthenticated attacker could open a large number of streams, leading to uncontrolled memory consumption and eventually causing an Out Of Memory (OOM) crash — especially in containerized or memory-constrained environments.

Impact

• Component: server_quic.go
• Attack Vector: Remote, network-based
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Impact: High availability loss (OOM kill or unresponsiveness)

This issue affects deployments with quic:// enabled in the Corefile. A single attacker can cause the CoreDNS instance to become unresponsive using minimal bandwidth and CPU.

Patches

The patch introduces two key mitigation mechanisms:

• max_streams: Caps the number of concurrent QUIC streams per connection. Default: 256.
• worker_pool_size: Introduces a server-wide, bounded worker pool to process incoming streams. Default: 1024.

This eliminates the 1:1 stream-to-goroutine model and ensures that CoreDNS remains resilient under high concurrency. The new configuration options are exposed through the quic Corefile block:

quic {
    max_streams 256
    worker_pool_size 1024
}

These defaults are generous and aligned with typical DNS-over-QUIC client behavior.

Workarounds

If you're unable to upgrade immediately, you can:

• Disable QUIC support by removing or commenting out the quic:// block in your Corefile
• Use container runtime resource limits to detect and isolate excessive memory usage
• Monitor QUIC connection patterns and alert on anomalies

References

• RFC 9250 - DNS over Dedicated QUIC Connections
• quic-go GitHub project
• QUIC stream exhaustion class of vulnerabilities (related)

Credit

Thanks to @thevilledev for disclovering this vulnerability and contributing a high-quality fix.

For more information

Please consult our security guide for more information regarding our security process.