CVE-2025-47950

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.

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.

• 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.

The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.

CVE-2025-47950 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.12.2); upgrading removes the vulnerable code path.

Kodem intelligence

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.

1. What is CVE-2025-47950? CVE-2025-47950 is a high-severity allocation of resources without limits or throttling vulnerability in github.com/coredns/coredns (go), affecting versions < 1.12.2. It is fixed in 1.12.2. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
2. How severe is CVE-2025-47950? CVE-2025-47950 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/coredns/coredns are affected by CVE-2025-47950? github.com/coredns/coredns (go) versions < 1.12.2 is affected.
4. Is there a fix for CVE-2025-47950? Yes. CVE-2025-47950 is fixed in 1.12.2. Upgrade to this version or later.
5. Is CVE-2025-47950 exploitable, and should I be worried? Whether CVE-2025-47950 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-47950 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-47950? Upgrade github.com/coredns/coredns to 1.12.2 or later.