Crash during DNSSEC validation of malicious content
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.
Problem Types
| Type | CWE ID | Description |
|---|
| CWE | CWE-824 | CWE-824: Access of Uninitialized Pointer |
Type: CWE
Description: CWE-824: Access of Uninitialized Pointer
Metrics
| Version | Base score | Base severity | Vector |
|---|
| 4.0 | 8.7 | HIGH | 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 |
Version: 4.0
Base score: 8.7
Base severity: HIGH
Vector: 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
Timeline
| Event | Date |
|---|
| Issue reported by Qifan Zhang | 2026-04-15 00:00:00 |
| NLnet Labs shares patch | 2026-04-29 00:00:00 |
| Qifan Zhang verifies patch | 2026-04-29 00:00:00 |
| Fixes released with version 1.25.1 | 2026-05-20 00:00:00 |
Event: Issue reported by Qifan Zhang
Date: 2026-04-15 00:00:00
Event: NLnet Labs shares patch
Date: 2026-04-29 00:00:00
Event: Qifan Zhang verifies patch
Date: 2026-04-29 00:00:00
Event: Fixes released with version 1.25.1
Date: 2026-05-20 00:00:00