CVE-2024-25583

What it actually does

Improper validation of responses from upstream servers in recursive forwarding mode allows a crafted packet to trigger a crash or resource exhaustion in the recursor process.

Why it matters to the business

Organizations relying on recursive forwarding experience intermittent or prolonged DNS resolution outages, disrupting dependent services until the recursor is restarted or the upstream source is isolated.

How an attack unfolds

An attacker positions a malicious or compromised upstream server in the forward-recurse chain and sends a specially formatted response that the recursor fails to handle safely, resulting in denial of service.

How to fix it

Disable recursive forwarding if not required, or apply the vendor-supplied update that corrects response validation when it becomes available; monitor upstream sources for unexpected behavior.

How to confirm the fix worked

Review recursor configuration for forward-recurse settings, replay known malformed responses in a test environment, and confirm the process remains stable after applying updates.

Typical attack path

1. Identify or compromise an upstream server used by the target recursor's forward-recurse configuration
2. Craft and transmit a malformed DNS response that triggers the validation flaw
3. Observe recursor crash or resource exhaustion leading to service unavailability

How to detect it

Search recursor logs for unexpected process terminations, malformed response handling errors, or restarts correlated with traffic from configured upstream servers.

What your security team should do

• Audit all recursor deployments for use of forward-recurse and disable where possible
• Prioritize patching once fixed versions are released given the high availability impact
• Implement network segmentation and upstream server allow-listing to reduce exposure
• Enable detailed logging and monitoring for recursor process restarts or crashes