Bug 2491822 (CVE-2026-56115)

Summary: CVE-2026-56115 dhcpcd: dhcpcd: Denial of Service via crafted DHCPv6 ADVERTISE message
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in dhcpcd. This vulnerability allows an unauthenticated attacker on the same network link to trigger a one-byte stack out-of-bounds write. By sending a specially crafted DHCPv6 ADVERTISE message with an oversized option, the attacker can corrupt adjacent stack memory. This can lead to a denial of service (DoS) in the affected system.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 2492038, 2492039    
Bug Blocks:    

Description OSIDB Bzimport 2026-06-23 17:03:48 UTC
dhcpcd through 10.3.2, fixed in commit 2f00c7b, contains a one-byte stack out-of-bounds write vulnerability in dhcp6_makemessage() in src/dhcp6.c that allows unauthenticated same-link attackers to write beyond a fixed local buffer by serializing an oversized RFC6603 OPTION_PD_EXCLUDE option body. Attackers can send a crafted DHCPv6 ADVERTISE message containing an IA_PD IAPREFIX /0 with a valid OPTION_PD_EXCLUDE using an exclude prefix length of /121 through /128 to trigger the out-of-bounds write and potentially corrupt adjacent stack memory.