CVE-2026-56444
Description
A Denial of Service (DoS) flaw exists in Unbound under specific serve-expired and discard-timeout configurations. By sending crafted queries, a remote attacker can exhaust an internal counter, causing the server to drop new legitimate client queries and degrade resolution services.
Statement
This Low-impact flaw in Unbound can lead to a denial of service. While a remote attacker could exhaust the reply address counter with specially crafted queries, Red Hat products are not affected by default. The vulnerability requires specific non-default serve-expired and discard-timeout configurations, which are not present in standard Red Hat deployments.
Mitigation
To mitigate this issue, ensure that Unbound is configured with `serve-expired-client-timeout` not greater than `discard-timeout` when `serve-expired: yes` is enabled. Alternatively, disable the `serve-expired` feature if it is not required. Red Hat's default configurations for Unbound prevent this vulnerability from being exploited.
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 | 5.9 |
| 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 | None | N/A | None |
| Availability Impact | Low | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (Other); DoS: Resource Consumption (Memory); DoS: Resource Consumption (CPU)
An attacker that can influence the allocation of resources that are not properly released could deplete the available resource pool and prevent all other processes from accessing the same type of resource. Frequently-affected resources include memory, CPU, disk space, power or battery, etc.
Frequently Asked Questions
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