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CVE-2026-42923

đŸ”ļ medium
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Summary

NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the DNSSEC validator where the code path to consult the negative cache for DS records does not take into account the limit on NSEC3 hash calculations introduced in 1.19.1. This leads to degradation of service during the attack. An adversary that controls a DNSSEC signed zone can exploit this by signing NSEC3 records with acceptably high iterations for child delegations and querying a vulnerable Unbound. Unbound will kee

Description

NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the DNSSEC validator where the code path to consult the negative cache for DS records does not take into account the limit on NSEC3 hash calculations introduced in 1.19.1. This leads to degradation of service during the attack. An adversary that controls a DNSSEC signed zone can exploit this by signing NSEC3 records with acceptably high iterations for child delegations and querying a vulnerable Unbound. Unbound will keep performing the allowed hash calculations on the NSEC3 records and will not limit the work by the mitigation introduced in 1.19.1. As a side effect, a global lock for the negative cache will be held for the duration of the hashing, blocking other threads that need to consult the negative cache. Coordinated attacks could raise the vulnerability to denial of service. Unbound 1.25.1 contains a patch with a fix to bound the vulnerable code path with the existing limit for NSEC3 hash calculations.

CVSS Score
5.3
Medium
EPSS Score
0.3
Exploit Probability
Published Date
2026-05-20
First Seen: 2026-05-21
📊 Relative Risk Intelligence

This CVE is Lower Risk - more severe than 19.2% of all 349,016 vulnerabilities in our database.

#282,016
Below average severity
Severity Percentile
đŸŽ¯ CISA SSVC Assessment Updated: May 20, 2026
🔍 Exploitation Status
None
No known exploits
⚙ī¸ Automatable
YES
Can be exploited automatically
đŸ’Ĩ Technical Impact
Partial
Limited system impact
🏆 Discovered By
Qifan Zhang (Palo Alto Networks)
SSVC data provided by CISA
Last Modified 2026-07-24
Source NVD 🔗
CVSS Vector 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
CVSS Vector 4.0 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/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:Amber
CWE IDs (Weakness Types)
CWE-407

đŸ“Ļ Affected Products 1

Vendor Product Status Affected Versions
nlnetlabs unbound Affected
> 1.19.1 < 1.25.1

🔗 References 1

https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-...
Mitigation Vendor Advisory

🔗 Related CVEs 6

CVE ID Severity CVSS EPSS Summary Published
CVE-2026-32665 ⚠ī¸ high 7.5 0.3 In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, when downstream DNS-over-QUIC (DoQ) is enabled, the first two b... 2026-07-22
CVE-2026-40691 ⚠ī¸ high 7.5 0.3 In Unbound 1.9.0 up to and including 1.25.1, when a DNSCrypt query is received over TCP, the routine that encrypts the r... 2026-07-22
CVE-2026-41637 ℹī¸ low 3.7 0.3 In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, client terminated DNS-over-QUIC (DoQ) queries are not accounted... 2026-07-22
CVE-2026-42955 ℹī¸ low 3.7 0.2 In NLnet Labs Unbound 1.16.2 up to and including 1.25.1, a similar vulnerability as with CVE-2026-40622 in the 'ghost do... 2026-07-22
CVE-2026-44621 đŸ”ļ medium 5.9 0.3 With NLnet Labs Unbound up to and including version 1.25.1, applications using libunbound and configured with 'unwanted-... 2026-07-22
CVE-2026-44687 ℹī¸ low 3.7 0.2 In NLnet Labs Unbound 1.13.2 up to and including 1.25.1, stub or forward zones where the name is below an intermediate l... 2026-07-22
These CVEs affect the same products