CVE-2026-42004
Deferred Deferred - Pending Action
EDNS OPT Record Rewriting Bypass in DNSdist

Publication date: 2026-06-25

Last updated on: 2026-06-25

Assigner: Open-Xchange

Description
An attacker can send a crafted EDNS OPT record that will be ignored by DNSdist’s filtering rules, but will be rewritten as a valid OPT record when EDNS Client Subnet is inserted, causing the backend to see the EDNS option(s) that DNSdist did not filter.
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Meta Information
Published
2026-06-25
Last Modified
2026-06-25
Generated
2026-06-25
AI Q&A
2026-06-25
EPSS Evaluated
N/A
NVD
CVE-2026-42004
EUVD
EUVD-2026-39351
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
open-xchange dnsdist *
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Exploitability
CWE
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KEV
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CWE ID Description
CWE-115 The product misinterprets an input, whether from an attacker or another product, in a security-relevant fashion.
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Executive Summary

This vulnerability involves DNSdist, where an attacker can send a specially crafted EDNS OPT record that bypasses DNSdist's filtering rules. Although DNSdist ignores this crafted record during filtering, it rewrites it as a valid OPT record when inserting the EDNS Client Subnet option. As a result, the backend server receives EDNS options that DNSdist was supposed to filter out but did not.

Impact Analysis

The impact of this vulnerability is limited to information integrity. Since the backend receives EDNS options that bypass filtering, it could lead to unintended processing of these options. According to the CVSS score, the impact on confidentiality is none, availability is none, but there is a low impact on integrity. The attack can be performed remotely without privileges or user interaction, but requires high attack complexity.

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