CVE-2026-42959: nlnet labs unbound Access of Uninitialized Pointer
Vulnerability summary
CVE-2026-42959 is a high (CVSS 8.7) Access of Uninitialized Pointer vulnerability in nlnet labs unbound. EPSS estimates a 0.72% chance of exploitation in the next 30 days, higher than 52.9% of scored vulnerabilities.
Advisory lineage
Upstream 0 · Downstream 9 · Related 7Timeline
- 20-05-2026PublishedVulnerability first disclosed.
- 01-09-2026Last modifiedVulnerability information updated.
Description
NLnet Labs Unbound up to and including version 1.25.0 has a denial of service vulnerability in the DNSSEC validator that can lead to a crash given malicious upstream replies. When Unbound constructs chase-reply messages for validation, the code uses the wrong counter to calculate write offsets for ADDITIONAL section rrsets. DNAME duplication could increase the ANSWER section count and authority filtering could decrease the AUTHORITY section count and create an uninitialized array slot. Combining these two, the validator later dereferences this uninitialized pointer, causing an immediate process crash. An adversary controlling a DNSSEC-signed domain can trigger this bug with a single query by configuring a DNAME chain with unsigned CNAMEs and a response containing unsigned AUTHORITY records alongside signed ADDITIONAL glue records. Unbound 1.25.1 contains a patch with a fix to use the proper counters to calculate the write offsets.
CVSS metrics
8 scores · 5 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated8.7HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/U:Red
- NVDNIST8.7HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Red
- OSV · AlpineEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- OSV · UbuntuEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- OSV · DebianEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- NVDNIST7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS trend
Probability
0.72%
Chance of exploitation in the next 30 days
Percentile
53%
Versus all other CVEs
30-day change
-0.06 pp
From 0.78% on 19-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Alpine1 product
- unbound< 1.25.2-r0 | < 1.25.1-r0
Debian1 product
- unboundAll versions (No fix recorded) | < 1.22.0-2+deb13u3 | < 1.25.1-1
Nlnet labs1 product
- unbound< 1.25.1
Nlnetlabs1 product
- unbound< 1.25.1
Ubuntu1 product
- unbound< 1.4.22-1ubuntu4.14.04.3+esm3 | < 1.5.8-1ubuntu1.1+esm3 | < 1.6.7-1ubuntu2.6+esm4 | < 1.9.4-2ubuntu1.11+esm1 | < 1.13.1-1ubuntu5.15 | < 1.19.2-1ubuntu3.8 | < 1.22.0-2ubuntu2.3 | < 1.24.2-1ubuntu2.1
5 vendors · 5 products
