CVE-2026-80225 — unbound
HIGHCVE-2026-80225 is a high-severity (CVSS 7.5) CWE-770 vulnerability. A fix is available — see the affected versions and patch details below.
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-80225.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-80225 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 386,684 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Description
In NLnetLabs Unbound up to and including 1.26.0, a degradation of service vulnerability is present in the TCP/DoT reading procedure where there is no limit on consecutive reads. A malicious actor that can stream and sustain a rate of distinct uncached names over the TCP/DoT connection, monopolizes a single worker's entire event loop for as long as its writes stay ahead of the drain.
Affected Products
unboundnlnetlabsDetection & mitigation playbook
VulnerabilityDetect
Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).
Fix
Upgrade the affected component to the fixed release for CVE-2026-80225, or apply your distribution's backported patch — distro builds are often patched at an older version number, so check your vendor's advisory rather than the upstream version alone.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
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 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…Source: Red Hat security advisory for CVE-2026-80225 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Hardened Images | unbound-main-1.26.1-1.hum1 | RHSA-2026:68590 |
Frequently Asked Questions
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