CVE-2026-32792: CWE-166: Improper Handling of Missing Special Element in NLnet Labs Unbound
NLnet Labs Unbound versions 1.6.2 through 1.25.0 have a denial of service vulnerability when compiled with DNSCrypt support. A specially crafted DNSCrypt query with decrypted plaintext of all zero bytes and missing an expected marker can cause Unbound to read beyond the intended buffer, potentially causing a heap overflow and crash. The likelihood of a crash is low and depends on the memory allocator and layout. Version 1.25.1 includes a patch that bounds the reading to prevent this issue.
AI Analysis
Technical Summary
The vulnerability in NLnet Labs Unbound (1.6.2 to 1.25.0) occurs when DNSCrypt support is enabled. A malicious DNSCrypt query lacking the expected 0x80 marker and containing only 0x00 bytes causes Unbound to read excessively from the DNSCrypt packet buffer. This can lead to a heap overflow due to underflow in the packet reading procedure, potentially causing a denial of service via crash. The exploitability depends on the underlying memory allocator and layout. Unbound 1.25.1 fixes this by bounding the read operations within the buffer.
Potential Impact
Successful exploitation can cause a denial of service by crashing the Unbound DNS resolver process. The heap overflow may lead to memory corruption, but the likelihood of a crash is low and no known exploits are reported in the wild. There is no indication of code execution or data leakage from this vulnerability.
Mitigation Recommendations
Upgrade to Unbound version 1.25.1 or later, which contains an official fix bounding the DNSCrypt packet reading to prevent heap overflow. No other mitigations are indicated. Patch status is confirmed by the vendor advisory stating the fix is included in version 1.25.1.
CVE-2026-32792: CWE-166: Improper Handling of Missing Special Element in NLnet Labs Unbound
Description
NLnet Labs Unbound versions 1.6.2 through 1.25.0 have a denial of service vulnerability when compiled with DNSCrypt support. A specially crafted DNSCrypt query with decrypted plaintext of all zero bytes and missing an expected marker can cause Unbound to read beyond the intended buffer, potentially causing a heap overflow and crash. The likelihood of a crash is low and depends on the memory allocator and layout. Version 1.25.1 includes a patch that bounds the reading to prevent this issue.
CVSS v4.0
Score 4.6medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in NLnet Labs Unbound (1.6.2 to 1.25.0) occurs when DNSCrypt support is enabled. A malicious DNSCrypt query lacking the expected 0x80 marker and containing only 0x00 bytes causes Unbound to read excessively from the DNSCrypt packet buffer. This can lead to a heap overflow due to underflow in the packet reading procedure, potentially causing a denial of service via crash. The exploitability depends on the underlying memory allocator and layout. Unbound 1.25.1 fixes this by bounding the read operations within the buffer.
Potential Impact
Successful exploitation can cause a denial of service by crashing the Unbound DNS resolver process. The heap overflow may lead to memory corruption, but the likelihood of a crash is low and no known exploits are reported in the wild. There is no indication of code execution or data leakage from this vulnerability.
Mitigation Recommendations
Upgrade to Unbound version 1.25.1 or later, which contains an official fix bounding the DNSCrypt packet reading to prevent heap overflow. No other mitigations are indicated. Patch status is confirmed by the vendor advisory stating the fix is included in version 1.25.1.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- NLnet Labs
- Date Reserved
- 2026-05-07T10:07:51.839Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a0d86fdba1db4736270ee4d
Added to database: 05/20/2026, 10:03:41 UTC
Last enriched: 05/28/2026, 21:17:48 UTC
Last updated: 07/31/2026, 19:22:58 UTC
Views: 56
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