CVE-2026-44621
Description
A flaw was found in libunbound, a library used by applications for DNS resolution. A remote attacker could exploit this vulnerability by sending specially crafted network traffic. This could cause applications using libunbound to terminate unexpectedly, leading to a denial of service (DoS). This occurs when the 'unwanted-reply-threshold' is configured, and the application attempts to call a cleanup function that is not properly allowed, resulting in a fatal exit.
Statement
A Moderate denial of service flaw exists in libunbound where applications configured with unwanted-reply-threshold can be terminated by specially crafted network traffic. This occurs when the libworker_alloc_cleanup function is called, which is not on the allow list for embedded applications. The unbound daemon itself is not affected as it uses a different, allowed function.
Mitigation
To mitigate this issue, ensure that any applications using `libunbound` do not set the `unwanted-reply-threshold` to a non-zero value. Disabling or setting this threshold to zero prevents the vulnerable code path from being triggered.
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).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | 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 | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
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: Crash, Exit, or Restart
An attacker that can trigger an assert statement can still lead to a denial of service if the relevant code can be triggered by an attacker, and if the scope of the assert() extends beyond the attacker's own session.
Frequently Asked Questions
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