Title: Operational Notification: ISC DHCP OMAPI interface memory usage attack
Document Version: 1.2
Posting date: 1st October 2026
Canonical URL: https://kb.isc.org/docs/isc-dhcp-omapi-interface-memory-usage-attack
Program impacted: ISC DHCP
Versions affected:
ISC DHCP
- 4.1-ESV-R1 -> 4.1-ESV-R16-P1
- 4.4.0 -> 4.4.3.
All branches of ISC DHCP are beyond their End-of-Life (EOL) and are no longer supported by ISC. ISC DHCP users are encouraged to migrate to its successor, Kea.
It is safe to assume that all versions after the introduction of OMAPI in ISC DHCP 3.0 are affected.
Description:
Due to a bug in the memory management, an unauthenticated remote attacker with access to a dhcpd server's OMAPI port may increase the server's memory usage without bounds.
Impact:
The allocated memory could grow large enough to affect system performance, and could trigger an automatic shutdown of the dhcpd process on systems with an "OOM killer" (out-of-memory killer) mechanism.
Solution:
As a workaround, secure the OMAPI port, restricting access to connections only from trusted hosts.
Access to the OMAPI port by unauthorized individuals is very dangerous, so it is important that access be restricted by firewall to only authorized equipment. This is always the best advice, even if the attack that is the subject here were not possible.
Acknowledgments:
ISC would like to thank Kimi Security Team (Moonshot AI) for bringing this vulnerability to our attention.
Related Documents:
- "Securing dhcpd against unauthorized OMAPI control connections"
- Migrating from ISC DHCP to Kea DHCP using the Migration Assistant
Do you still have questions? Questions regarding this notification should go to security-officer@isc.org. To report a new issue, please encrypt your message using security-officer@isc.org's PGP key which can be found here: https://www.isc.org/pgpkey/. If you are unable to use encrypted email, you may also report new issues at: https://www.isc.org/reportbug/.
Note:
ISC patches only currently supported versions. When possible we indicate EOL versions affected. (For current information on which versions are actively supported, please see https://www.isc.org/download/.)
ISC Security Vulnerability Disclosure Policy:
Details of our current security advisory policy and practice can be found in the ISC Software Defect and Security Vulnerability Disclosure Policy at https://kb.isc.org/docs/aa-00861.
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