Heap-based buffer overflow in Unbound - CVE-2026-56416
Published: July 23, 2026
Vulnerability identifier: #VU139219
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-56416
CWE-ID: CWE-122
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: NLnet Labs
Affected software:
Unbound
Unbound
Detailed vulnerability description
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to a heap-based buffer overflow in query_dname_tolower() when validating DNSSEC-signed PX, RP, MINFO, or SOA RRsets with truncated multi-dname RDATA. A remote attacker can serve a specially crafted DNS record with an absent second domain name to cause a denial of service.
Exploitation requires control of a DNSSEC-signed authoritative server, and the outcome depends on heap memory layout and buffer contents.
How to mitigate CVE-2026-56416
Install security update from vendor's website.