CVE-2026-53921
odhcpd: Stack buffer overflow in DHCPv6 IA reply serialization (2 independent sites)
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.
INFO
Published Date :
Oct. 23, 2026, 2:17 p.m.
Last Modified :
Oct. 23, 2026, 2:17 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
Affected Products
The following products are affected by CVE-2026-53921
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | CRITICAL | MITRE-CVE | ||||
| CVSS 3.1 | CRITICAL | [email protected] |
Solution
- Update odhcpd to version 25.12 or later.
- Apply vendor patches for odhcpd.
- Restart the odhcpd service.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-53921.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-53921 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-53921
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-53921 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-53921 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by [email protected]
Oct. 23, 2026
Action Type Old Value New Value Added 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Added CWE CWE-121 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/53xxx/CVE-2026-53921.json">CVE-2026-53921</a> Added Reference https://github.com/openwrt/odhcpd/commit/0320032ae313452f3c8cb8725c621dd06c36dc03 Added Reference https://github.com/openwrt/odhcpd/commit/03dacc23356b5789842b9d1bba0200fd005e35f3 Added Reference https://github.com/openwrt/odhcpd/commit/2a42d34c3615e2449ca273f673eee7c429d819a9 Added Reference https://github.com/openwrt/odhcpd/commit/6634b7a3c79c41a27687925c98c35c8aea2f2b5a Added Reference https://github.com/openwrt/odhcpd/commit/d168c27fb6a55a07ac4c888e09ff2f41e263d7b7 Added Reference https://github.com/openwrt/odhcpd/commit/d329a15413387027453644cd363dca06ade28328 Added Reference https://github.com/openwrt/odhcpd/security/advisories/GHSA-7fwx-hhrg-3496