# CVE-2026-42944

## Summary

- **CVE ID:** CVE-2026-42944
- **Severity:** HIGH
- **CVSS Score:** 8.7 (CVSS: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)
- **CWE:** CWE-197, CWE-787
- **Published:** May 20, 2026
- **Last Modified:** Aug 26, 2026

## Description

NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a vulnerability that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation.

## Affected Products

- NLnet Labs — Unbound (1.14.0)

## References

- [CNA](https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42944.txt)
- [redhat-SADP](https://access.redhat.com/security/cve/CVE-2026-42944)
- [redhat-SADP](https://bugzilla.redhat.com/show_bug.cgi?id=2479774)
- [redhat-SADP](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42944.json)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:23231)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:24365)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:24369)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:19752)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.84%
- **EPSS Percentile:** 55.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._