# CVE-2026-55990: Packet of death for a DNSCrypt misconfigured Unbound

CVE-2026-55990 is fixed in unbound on 1 platform, first by DEBIAN-CVE-2026-55990, released July 28, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-55990
- Priority: Routine
- CVSS: 5.9 (Moderate)
- EPSS: 0.0025
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 22, 2026
- Weakness: Use of Uninitialized Variable
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55990

## Description

In NLnet Labs Unbound 1.7.0 up to and including 1.25.1, when the 'dnscrypt:' clause lists more 'dnscrypt-provider-cert:' files than there are matching 'dnscrypt-secret-key:' files, Unbound fills only the matched prefix and leaves the tail slots at the '0xdb' fill that libsodium's allocator writes into every allocation. Unbound would then iterate over the number of cert files, not the actual slots, so it walks into a slot with garbage data filled with '0xdb' bytes. Any unauthenticated client that sends one UDP datagram of ≥ 68 bytes whose first 8 bytes are '0xdb' to 'dnscrypt-port' will use that garbage entry which leads to a garbage dereference killing the server. This is a silent faulty configuration that goes unnoticed until triggered with the right client query. Unbound needs to be compiled with DNSCrypt support ('--enable-dnscrypt').

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | unbound Debian 13.5 (trixie) | 1.26.1-0+deb13u1 | [DEBIAN-CVE-2026-55990](https://patchblox.com/security/data/fix/linux/debian-cve-2026-55990.md) | Jul 28, 2026 |
| Linux | unbound Debian 14 | 1.25.2-1 | [DEBIAN-CVE-2026-55990](https://patchblox.com/security/data/fix/linux/debian-cve-2026-55990.md) | Jul 28, 2026 |
| Linux | unbound opensuse-leap 16.0 | 1.25.2-160000.1.1 | [OPENSUSE-SU-2026:21550-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21550-1.md) | Aug 10, 2026 |
| Linux | unbound sles 15.6 | 1.25.2-150600.23.19.1 | [SUSE-SU-2026:3885-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3885-1.md) | Aug 31, 2026 |
| Linux | unbound sles 15.7 | 1.25.2-150600.23.19.1 | [SUSE-SU-2026:3885-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3885-1.md) | Aug 31, 2026 |
| Linux | unbound sles 16.0 | 1.25.2-160000.1.1 | [SUSE-SU-2026:23226-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23226-1.md) | Aug 10, 2026 |

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Data as of 2026-11-08T19:12:23Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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