CVE-2026-101338

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Remote Code Execution in NSD DNS Server

Publication date: 2026-10-14

Last updated on: 2026-10-16

Assigner: NLnet Labs

Description

When a SVCB or HTTPS RR has filled the wire format RDATA up to the brim, another ECH parameter may overwrite the stack, and once beyond the limit, the base64 decoder can write attacker controlled data of unlimited size. Zone files which are written out by NSD itself, such as for zones for which the NSD instance is secondary, will not be formatted like this. The zone file must be fed to NSD directly, (but it could come, for example, from an operator controlled provisioning system).

CVSS Scores

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Meta Information

Published

2026-10-14

Last Modified

2026-10-16

Generated

2026-10-19

AI Q&A

2026-10-15

EPSS Evaluated

2026-10-18

NVD

CVE-2026-101338

EUVD

EUVD-2026-100983

Affected Vendors & Products

Vendor	Product	Version / Range
NLnet	Labs	NSD 4.10.0

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-121	A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

Attack-Flow Graph

Executive Summary

This vulnerability involves a stack overwrite in NSD when processing specially crafted SVCB or HTTPS resource records. When the wire format RDATA is filled completely, an additional ECH parameter can overwrite the stack, allowing the base64 decoder to write attacker-controlled data of unlimited size. This could potentially lead to arbitrary command execution.

Detection Guidance

This vulnerability affects NSD versions 4.10.0 to 4.15.2. To detect it, check your NSD version with 'nsd -v'. If you are running a vulnerable version, inspect zone files for malformed SVCB or HTTPS records that may trigger the issue.

Impact Analysis

If exploited, this vulnerability could allow attackers to execute arbitrary commands on the system running NSD. This could lead to unauthorized access, data breaches, or further compromise of the affected system. The impact depends on the privileges of the NSD service.

Compliance Impact

This vulnerability could lead to unauthorized access or data breaches, which may violate compliance requirements under GDPR, HIPAA, or other regulations. Organizations using affected NSD versions may face legal and regulatory penalties if exploited.

Mitigation Strategies

Upgrade NSD to version 4.15.3 or apply the manual patch for 4.15.2 using 'patch -p1 < patch_CVE-2026-101338.diff' followed by 'make install'.
Avoid feeding untrusted zone files directly into NSD. Validate zone files from external sources before processing.

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