CVE-2026-82720
MEDIUMDescription
NLnet Labs Unbound 1.12.0 up to and including 1.26.0 has a use-after-free vulnerability when compiled for DNS-over-HTTPs support with '--with-libnghttp2'. During failure code paths (i.e., RPZ drop query, jostle due to heavy traffic), a dropped DoH stream brings down the whole DoH session and does not account properly for other DoH streams in the same session. This leads to use-after-free in those code paths. If the prerequisites are satisfied (possible RPZ drop or heavy client traffic), a malicious actor can trigger the vulnerability with a single DoH connection and the appropriate traffic. Impact is limited as the reads are not user controlled and the use-after-free leads to early returns. However, a hardened allocator can catch the use-after-free and controllably terminate the process resulting to denial of service.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Exploit Intelligence
Low risk: more likely to be exploited than 21% of all known CVEs.
References
Related Vulnerabilities
Other CWE-416 (Use After Free) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2019-0708 | Critical | 9.8 | 100% | KEV + Ransom | - |
| CVE-2021-31166 | Critical | 9.8 | 100% | KEV | Fix |
| CVE-2015-5119 | Critical | 9.8 | 99% | KEV | - |
| CVE-2010-3962 | High | 8.1 | 97% | KEV | - |
| CVE-2021-34833 | High | 7.8 | 96% | - | - |
| CVE-2015-0313 | Critical | 9.8 | 95% | KEV | Fix |
Common questions
How do I fix CVE-2026-82720?
Upgrade unbound on debian unstable to 1.26.1-1 or later.
Is CVE-2026-82720 being actively exploited?
Not that we know of. CVE-2026-82720 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.29% is the estimated probability that it will be exploited in the next 30 days. That is higher than 21% of all scored CVEs.
How severe is CVE-2026-82720?
CVE-2026-82720 has a CVSS v3 base score of 5.9, rated moderate. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2026-82720 affect?
Published advisories record a fix for unbound (Debian). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-09-16.