Critical severity · published Oct 23, 2026
CVE-2026-53921
odhcpd: Stack buffer overflow in DHCPv6 IA reply serialization (2 independent sites)
New
9.8
CVSS
1.1%
EPSS
No
On KEV
Description
odhcpd is the DHCPv6, DHCPv4, and router-advertisement server used by OpenWrt. Prior to version 25.12, odhcpd's DHCPv6 IA response handler writes past the end of a fixed 512-byte stack buffer (pdbuf) when a single DHCPv6 REQUEST carries enough IA options to nearly exhaust the reply space. Two independent overflow sites exist in the same call chain, both reachable from the network via a single unauthenticated UDP packet. odhcpd runs as root on OpenWrt; embedded targets often lack stack canaries and ASLR, making code execution realistic. This issue has been patched in version 25.12.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)1.1% · higher than 66% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
OD
odhcpd · openwrt
< 25.12 · source: vendor
In the news
VulnerabilityCritical
Critical OpenWrt DHCPv6 Flaw Could Let Unauthenticated Attackers Run Code as Root
OpenWrt has shipped version 24.10.8 to close a critical DHCPv6 stack overflow and a wider set of remotely triggerable flaws in network services enabled by default.
The critical issue, tracked as CVE-2026-53921 and rated 9.8 on CVSS 3.1 in OpenWrt's GitHub advisory, lets an unauthenticated attacker able to reach the DHCPv6 server overwrite a stack buffer in odhcpd through a crafted DHCPv6
Jul 28, 2026·The Hacker News
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-53921
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-53921
github.com
https://github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621dd06c36dc03
github.com
https://github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200fd005e35f3
github.com
https://github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7c429d819a9
github.com
https://github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c8aea2f2b5a
github.com
https://github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b7
github.com
https://github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade28328
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