CVE-2026-33278
NLnet Labs Unbound 1.19.1 up to and including version 1.25.0 has a vulnerability in the DNSSEC validator that enables denial of service and possible remote code execution as a result of deep copying a data structure and erroneously overwriting a…
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (1.27%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
NLnet Labs Unbound 1.19.1 up to and including version 1.25.0 has a vulnerability in the DNSSEC validator that enables denial of service and possible remote code execution as a result of deep copying a data structure and erroneously overwriting a destination pointer. An adversary can exploit the vulnerability by controlling a malicious signed zone and querying a vulnerable Unbound. When DS sub-queries need to suspend validation due to NSEC3 computational budget exhaustion (introduced in Unbound 1.19.1), Unbound deep-copies response messages to preserve them across memory region teardown. A struct-assignment bug overwrites the destination's pointer with the source's pointer. After the sub-query region is freed, the resumed validator dereferences this dangling pointer, triggering a crash or potentially enabling arbitrary code execution. Unbound 1.25.1 contains a patch with a fix to preserve the correct pointer when deep copying the data structure.
- CVSS 4.0
- 9.1 CRITICALCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 1.27% probability · 68th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-416, CWE-672
- Affected
- nlnetlabs/unbound
- Source
- sep@nlnetlabs.nl
References
- https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-33278.txtMitigation, Vendor Advisory
- https://access.redhat.com/errata/RHSA-2026:19752
- https://access.redhat.com/errata/RHSA-2026:23231
- https://access.redhat.com/errata/RHSA-2026:24369
- https://access.redhat.com/security/cve/CVE-2026-33278
- https://bugzilla.redhat.com/show_bug.cgi?id=2479808
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33278.json
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.