CVE-2026-54478
Description
A flaw was found in Unbound. When Unbound is configured to listen on a proxy-protocol port with DNS cookies enabled, it incorrectly computes the server cookie using the proxy's network address instead of the actual client's address. This vulnerability allows an off-path attacker to harvest a valid server cookie and replay it from a spoofed source, effectively bypassing DNS Cookie security checks intended to prevent DNS spoofing.
Statement
This Low impact flaw in Unbound occurs when the DNS resolver is configured to use both proxy-protocol-port and answer-cookie: yes. The server cookie is incorrectly derived from the proxy's address, enabling an off-path attacker to bypass DNS Cookie security by replaying a harvested cookie. This vulnerability requires a specific, non-default configuration and has high attack complexity, limiting its impact.
Mitigation
To mitigate this issue, avoid enabling `answer-cookie: yes` when Unbound is configured to listen on a `proxy-protocol-port`. If the `proxy-protocol-port` is essential, consider disabling DNS cookies. If both features are required, ensure the proxy infrastructure is secured and trusted. A restart of the Unbound service is required for configuration changes to take effect.
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 | 3.7 | N/A | 3.7 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | Low | N/A | Low |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
Frequently Asked Questions
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