CVE-2026-50252
Description
A flaw in Unbound's SO_REUSEPORT implementation reduces UDP source port entropy by allowing attackers to map ports to specific worker threads. This enables DNS cache poisoning, potentially leading to traffic redirection or unauthorized information disclosure.
Statement
Moderate: This flaw allows for DNS cache poisoning due to predictable UDP source ports when Unbound's so-reuseport option is enabled by default. An attacker on an adjacent network can exploit this to compromise the integrity of DNS resolutions, leading to potential redirection of traffic.
Mitigation
Disable the so-reuseport option by explicitly setting so-reuseport: no in your unbound.conf file. This prevents the deterministic mapping of worker threads to outbound UDP source ports, effectively stopping the cache poisoning vector. Additionally, restrict who can query the resolver using the access-control directive to reduce the overall attack surface, and restart the Unbound service to apply the changes.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.5 | 9.3 | N/A |
| Attack Vector | Adjacent Network | Adjacent Network | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Changed | N/A |
| Confidentiality | None | None | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | None | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
NVD: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:H
Understanding the Weakness (CWE)
Access Control,Integrity
Technical Impact: Bypass Protection Mechanism; Modify Application Data
An attacker could package untrusted data with trusted data to bypass protection mechanisms to gain access to and possibly modify sensitive data.
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