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

Summary

CVE	CVE-2026-93009
State	PUBLISHED
Assigner	redhat
Source Priority	CVE Program / NVD first with legacy fallback
Published	2026-10-29 14:18:00 UTC
Updated	2026-10-30 08:17:00 UTC
Description	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.

Risk And Classification

Primary CVSS: v3.1 4.3 MEDIUM from [email protected]

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

Problem Types: CWE-125 | CWE-125 Out-of-bounds Read

Version	Source	Type	Score	Severity	Vector
3.1	[email protected]	Secondary	4.3	MEDIUM	`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`
3.1	CNA	CVSS	4.3	MEDIUM	`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`

CVSS v3.1 Breakdown

Attack Vector

Adjacent

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

None

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

Vendor Declared Affected Products

Source	Vendor	Product	Version	Platforms
CNA	Red Hat	Red Hat Ceph Storage 9	Not specified	Not specified
CNA	Red Hat	Red Hat Enterprise Linux 10	Not specified	Not specified
CNA	Red Hat	Red Hat Enterprise Linux 6	Not specified	Not specified
CNA	Red Hat	Red Hat Enterprise Linux 7	Not specified	Not specified
CNA	Red Hat	Red Hat Enterprise Linux 8	Not specified	Not specified
CNA	Red Hat	Red Hat Enterprise Linux 9	Not specified	Not specified
CNA	Red Hat	Red Hat OpenShift Container Platform 4	Not specified	Not specified
CNA	Red Hat	Red Hat OpenShift Container Platform 4	Not specified	Not specified
CNA	Red Hat	Red Hat OpenShift Container Platform 4	Not specified	Not specified
CNA	Red Hat	Red Hat OpenShift Container Platform 4	Not specified	Not specified
CNA	Red Hat	Red Hat OpenShift Container Platform 5	Not specified	Not specified
CNA	Red Hat	Red Hat OpenShift Container Platform 5	Not specified	Not specified
CNA	Red Hat	Red Hat OpenStack Platform 13 Queens	Not specified	Not specified
CNA	Red Hat	Red Hat OpenStack Platform 18.0	Not specified	Not specified

References

Reference	Source	Link	Tags
access.redhat.com/security/cve/CVE-2026-93009	[email protected]	access.redhat.com
bugzilla.redhat.com/show_bug.cgi	[email protected]	bugzilla.redhat.com
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis

Vendor Comments And Credit

Discovery Credit

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

Additional Advisory Data

Source	Time	Event
CNA	2026-09-14T00:00:00.000Z	Reported to Red Hat.
CNA	2026-10-28T09:30:00.000Z	Made public.

Workarounds

CNA: 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>.

There are currently no legacy QID mappings associated with this CVE.