CVE-2026-55990: CWE-457: Use of Uninitialized Variable in NLnet Labs Unbound
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').
AI Analysis
Technical Summary
In NLnet Labs Unbound versions 1.7.0 through 1.25.1 compiled with DNSCrypt support, a configuration mismatch where more 'dnscrypt-provider-cert:' files are listed than 'dnscrypt-secret-key:' files causes Unbound to iterate over uninitialized memory slots filled with 0xdb bytes from libsodium's allocator. When an unauthenticated client sends a UDP datagram of at least 68 bytes starting with 0xdb bytes to the DNSCrypt port, Unbound dereferences this garbage data, resulting in a server crash. This vulnerability is due to use of uninitialized variables (CWE-457) and manifests as a denial of service condition triggered by malformed client queries.
Potential Impact
The vulnerability allows any unauthenticated client to cause a denial of service by crashing the Unbound DNS server via a specially crafted UDP datagram to the DNSCrypt port. There is no impact on confidentiality or integrity. The issue arises only with faulty DNSCrypt configuration and when Unbound is compiled with DNSCrypt support enabled.
Mitigation Recommendations
No official patch or remediation level is currently documented. Users should verify their DNSCrypt configuration to ensure the number of 'dnscrypt-provider-cert:' files does not exceed the number of 'dnscrypt-secret-key:' files. Until an official fix is released, avoid configurations that trigger this condition or disable DNSCrypt support if not required. Monitor vendor advisories for updates regarding an official fix.
CVE-2026-55990: CWE-457: Use of Uninitialized Variable in NLnet Labs Unbound
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').
CVSS v3.1
Score 5.9medium
Affected software
Run on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
In NLnet Labs Unbound versions 1.7.0 through 1.25.1 compiled with DNSCrypt support, a configuration mismatch where more 'dnscrypt-provider-cert:' files are listed than 'dnscrypt-secret-key:' files causes Unbound to iterate over uninitialized memory slots filled with 0xdb bytes from libsodium's allocator. When an unauthenticated client sends a UDP datagram of at least 68 bytes starting with 0xdb bytes to the DNSCrypt port, Unbound dereferences this garbage data, resulting in a server crash. This vulnerability is due to use of uninitialized variables (CWE-457) and manifests as a denial of service condition triggered by malformed client queries.
Potential Impact
The vulnerability allows any unauthenticated client to cause a denial of service by crashing the Unbound DNS server via a specially crafted UDP datagram to the DNSCrypt port. There is no impact on confidentiality or integrity. The issue arises only with faulty DNSCrypt configuration and when Unbound is compiled with DNSCrypt support enabled.
Mitigation Recommendations
No official patch or remediation level is currently documented. Users should verify their DNSCrypt configuration to ensure the number of 'dnscrypt-provider-cert:' files does not exceed the number of 'dnscrypt-secret-key:' files. Until an official fix is released, avoid configurations that trigger this condition or disable DNSCrypt support if not required. Monitor vendor advisories for updates regarding an official fix.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- NLnet Labs
- Date Reserved
- 2026-06-22T10:11:10.529Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a60c4249c2644c7f80e9263
Added to database: 07/22/2026, 13:22:44 UTC
Last enriched: 07/22/2026, 13:38:25 UTC
Last updated: 07/22/2026, 23:21:19 UTC
Views: 8
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
External Links
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.