Bug 2370860 (CVE-2025-47950)

Summary: CVE-2025-47950 coredns: CoreDNS Vulnerable to DoQ Memory Exhaustion via Stream Amplification
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: alcohan, gparvin, njean, owatkins, pahickey, rhaigner
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A memory exhaustion vulnerability was found in CoreDNS when operating with QUIC traffic streams. The CoreDNS server in affected versions would spawn a new goroutine for each incoming QUIC stream without limit. This flaw allows a malicious user to create an unbounded number of QUIC streams and consume all available resources, leading to an application level denial of service.
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Description OSIDB Bzimport 2025-06-06 18:01:12 UTC 
CoreDNS is a DNS server that chains plugins. In versions prior to 1.21.2, 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 1.21.2 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.