CVE-2026-93009 PUBLISHED

Dnsmasq: dnsmasq: heap out-of-bounds read in dhcpv6 option 39 fqdn decoder

Assigner: redhat
Reserved: 17.09.2026 Published: 29.10.2026 Updated: 29.10.2026

A flaw was found in dnsmasq. The DHCPv6 client hostname parser can read one byte past the end of a crafted FQDN option because it checks the next label length before confirming the pointer is still inside the option. An attacker on the local network can trigger this with a single DHCPv6 packet. The extra byte is not returned to the client or logged, and no crash has been demonstrated.

Metrics

CVSS Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
CVSS Score: 4.3

Product Status

Vendor Red Hat
Product Red Hat Ceph Storage 9
Versions Default: affected
Vendor Red Hat
Product Red Hat Enterprise Linux 10
Versions Default: affected
Vendor Red Hat
Product Red Hat Enterprise Linux 6
Versions Default: affected
Vendor Red Hat
Product Red Hat Enterprise Linux 7
Versions Default: affected
Vendor Red Hat
Product Red Hat Enterprise Linux 8
Versions Default: affected
Vendor Red Hat
Product Red Hat Enterprise Linux 9
Versions Default: affected
Vendor Red Hat
Product Red Hat OpenShift Container Platform 4
Versions Default: affected
Vendor Red Hat
Product Red Hat OpenShift Container Platform 4
Versions Default: affected
Vendor Red Hat
Product Red Hat OpenShift Container Platform 4
Versions Default: affected
Vendor Red Hat
Product Red Hat OpenShift Container Platform 4
Versions Default: affected
Vendor Red Hat
Product Red Hat OpenStack Platform 13 (Queens)
Versions Default: affected
Vendor Red Hat
Product Red Hat OpenStack Platform 18.0
Versions Default: affected

Workarounds

The following measures reduce risk:

  1. If DHCPv6 is not required, do not configure any IPv6 dhcp-range.
  2. Compile without DHCPv6 using COPTS=-DNO_DHCP6 if IPv6 DHCP is not needed.
  3. Restrict dnsmasq to trusted interfaces with --interface=<iface>.

Credits

  • Red Hat would like to thank Shubham Raj (Causal Security) for reporting this issue.

References

Problem Types

  • Out-of-bounds Read CWE