CVE-2026-56416 Affecting libunbound8 package, versions <1.25.2-150100.10.28.1


Severity

Recommended
0.0
medium
0
10

Based on SUSE Linux Enterprise Server security rating.

Threat Intelligence

EPSS
0.12% (2nd percentile)

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  • Snyk IDSNYK-SLES155-LIBUNBOUND8-19681314
  • published11 Sept 2026
  • disclosed31 Aug 2026

Introduced: 31 Aug 2026

CVE-2026-56416  (opens in a new tab)

How to fix?

Upgrade SLES:15.5 libunbound8 to version 1.25.2-150100.10.28.1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream libunbound8 package and not the libunbound8 package as distributed by SLES. See How to fix? for SLES:15.5 relevant fixed versions and status.

In NLnet Labs Unbound up to and including version 1.25.1, when the validator builds the canonical RDATA form for an RRSIG-covered PX/RP/MINFO/SOA RRset, it computes the address of the second embedded domain name as 'datstart + dname_valid(datstart, ...)' and passes it straight to 'query_dname_tolower()' without checking that a second name is actually present in the RDATA. The wire-format parser accepts multi-dname RRs whose RDATA ends after the first name, so an attacker who runs a DNSSEC-signed authoritative server can deliver a record with an absent second domain name (e.g. SOA record) and cause 'query_dname_tolower()' to walk label-by-label through stale bytes in the per-worker 'env->scratch_buffer', past the end of that heap allocation if 'msg-buffer-size' has been lowered from the default. This leads to heap buffer overflow and on a release build the outcome relies heavily on the contents of the buffer tail and the adjacent heap chunk.

CVSS Base Scores

version 3.1