CVE-2026-80225
Description
A flaw was found in Unbound. A malicious actor can exploit a vulnerability in the TCP/DoT reading procedure, which lacks a limit on consecutive reads. By continuously streaming distinct uncached names over a TCP/DoT connection, an attacker can monopolize a worker's event loop. This can lead to a degradation of service, effectively causing a Denial of Service (DoS) for legitimate users.
Statement
This Moderate severity flaw in Unbound allows a remote attacker to cause a denial of service by continuously sending distinct, uncached DNS queries over a TCP or DNS-over-TLS (DoT) connection. This can monopolize a single worker's event loop, leading to service degradation for legitimate users. The impact is limited to availability and requires sustained malicious traffic.
Mitigation
To mitigate this issue, restrict network access to the Unbound DNS resolver to only trusted clients and networks. This can be achieved by configuring firewall rules to limit inbound connections to the Unbound service ports (e.g., TCP port 53 for DNS over TCP, TCP port 853 for DNS over TLS). For example, using `firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="<TRUSTED_NETWORK>" port port="53" protocol="tcp" accept'` and `firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="<TRUSTED_NETWORK>" port port="853" protocol="tcp" accept'`. After adding rules, apply them with `firewall-cmd --reload`. Replace `<TRUSTED_NETWORK>` with the IP address or network range of trusted clients. Reloading firewall rules may temporarily interrupt network connections.
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 | 5.3 | 7.5 | 5.3 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | Low | Low | Low |
| Privileges Required | None | None | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | None | None | None |
| Integrity Impact | None | None | None |
| Availability Impact | Low | High | Low |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Resource Consumption (Other); Reduce Performance
This issue can make the product perform more slowly. If an attacker can influence the number of iterations in the loop, then this performance problem might allow a denial of service by consuming more platform resources than intended.
Frequently Asked Questions
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