CVE-2026-12245 NLnet Labs CVE debrief

Who should care

Defenders responsible for NSD deployments should assess exposure and prioritize remediation. This includes verifying inventory for potential exposure to CVE-2026-12245, assessing and applying patches or mitigations, and monitoring for and responding to potential crashes of the server process. Operational impacts include verifying inventory, assessing and applying patches or mitigations to prevent server crashes, and monitoring for and responding to server

Why it matters

CVE-2026-12245 is a heap use-after-free bug in NSD that causes server crashes on TLS connections. Defenders should assess exposure, prioritize remediation, and verify inventory for NSD deployments.

• Verify inventory for potential exposure to CVE-2026-12245
• Assess and apply patches or mitigations to prevent server crashes
• Monitor for and respond to potential crashes of the server process

Technical summary

CVE-2026-12245 is a heap use-after-free bug in NSD, affecting versions 4.13.0 and prior to 4.14.3. The bug causes a crash of the server process when logging errors on TLS connections, which can be triggered by sending a DNS query over a DoT connection and closing it without reading the response. This issue has a high CVSS score of 8.7, indicating a severe vulnerability. Defenders should prioritize verifying NSD inventory, assessing exposure to CVE-2026-12245, and applying patches or mitigations as needed. The vulnerability can be triggered trivially, emphasizing the need for swift action.

Defensive priority

Defenders should prioritize verifying NSD inventory, assessing exposure to CVE-2026-12245, and applying patches or mitigations as needed.

Recommended defensive actions

• Verify NSD inventory for potential exposure
• Assess and apply patches or mitigations for CVE-2026-12245
• Monitor for and respond to potential crashes of the server process
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and NVD entry provide details on the heap use-after-free bug in NSD. The vendor advisory from nlnetlabs provides patch information. Defenders should verify NSD inventory and assess exposure to CVE-2026-12245. The bug affects versions 4.13.0 and prior to 4.14.3. Limited source detail is available; explicit evidence limits apply.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.