OpenWrt odhcpd: Stack memory disclosure via short DHCPv6 IA_NA/IA_PD option
Summary
odhcpd, the DHCPv6, DHCPv4 and router advertisement server used by OpenWrt, reads the IAID field of a short IA_NA or IA_PD option before checking the option length. A network-adjacent client can send such an option and receive adjacent stack memory reflected in the DHCPv6 reply, which may include the stack canary and data useful for defeating ASLR. The issue requires DHCPv6 server handling to be enabled on the interface and a valid Client Identifier in the packet.
Affected
- OpenWrt odhcpd from 17.01.0 before 25.12.3
- Stable OpenWrt branches 22.03, 23.05 and 24.10 are covered by the advisory mapping
Fixed in
- Fixed in odhcpd 25.12.3 (CNA record)
- Fix commits: 719fc3abc0d7e7059871f9f572fb05ada86b8ff2 and f2275efc72a87a95f971f159babcbadc5d241d42
- OpenWrt 25.12.5 release notes also list the fix
- Fixed releases for other branches: Unknown.
Workaround
- Unknown. Disable DHCPv6 server handling on interfaces where it is not required.
Exploitation
- CISA SSVC: exploitation none, automatable yes, technical impact partial.
- No public exploitation confirmed in the sources reviewed.
- Attack requires access to the local IPv6 link.
Our recommendation
- Update odhcpd to the latest 25.12.x release, or to a release that includes the fix.
- Check whether DHCPv6 server functions are enabled on your OpenWrt devices and disable them where not needed.
- Restrict untrusted devices from the local network segment and monitor DHCPv6 traffic for unusual short IA options.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- GitHub Security Advisory GHSA-p769-5v73-pc4f github.com
- Fix commit 719fc3a github.com
- Fix commit f2275ef github.com
- OSV entry CVE-2026-53920 vulners.com
- Strix CVE record www.strix.ai
- OpenWrt 25.12.5 release notes (newreleases.io) newreleases.io
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 00:28.
Original description (NVD)
odhcpd is the DHCPv6, DHCPv4, and router-advertisement server used by OpenWrt. From version 17.01.0 to before version 25.12.3, odhcpd's DHCPv6 IA parser accepts an IA_NA or IA_PD option whose body is shorter than struct dhcpv6_ia_hdr, casts the option header to that full structure, and reads ia->iaid before proving that the IA body contains the IAID field. If an unauthenticated network-adjacent client places a zero-length or otherwise short IA option at the end of odhcpd's 8192-byte receive stack buffer, the IAID read crosses from data_buf into adjacent stack memory. The disclosed bytes are then reflected in the DHCPv6 reply IAID; prior ARM validation showed data_buf[8192:8196] disclosing the saved stack canary, and wider stack scans can leak ASLR-useful stack/process contents. This issue has been patched in version 25.12.3.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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