CVE-2026-78227
published 2026-09-16CVE-2026-78227: NLnet Labs Unbound 1.22.0 up to and including 1.26.1, has a use-after-free vulnerability when compiled for DNS-over-QUIC support with '--with-libngtcp2'. Each…
PriorityP340medium6.5CVSS 3.1
AVNACHPRNUINSUCHINAL
EPSS
0.34%
25.0th percentile
NLnet Labs Unbound 1.22.0 up to and including 1.26.1, has a use-after-free vulnerability when compiled for DNS-over-QUIC support with '--with-libngtcp2'. Each DoQ stream owns an output buffer that holds the DNS response. ngtcp2's retransmission buffer keeps a shallow pointer into the output buffer for as long as a STREAM frame may be resent. On a client RESET_STREAM, the output buffer is freed but ngtcp2 still holds the matching retransmission entries. The next PTO timeout makes ngtcp2 re-encode the STREAM frame and copy from the freed buffer. A malicious actor that can query Unbound over DoQ and that withholds ACKs, sends RESET_STREAM, and waits for PTO, reaches this use-after-free with no privilege. This leads to retransmissions against freed memory and eventually an abnormal server exit under a 20-query spray.
Affected
4 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| nlnet_labs | unbound | >= 1.22.0 < 1.26.1 | 1.26.1 |
| nlnetlabs | unbound | >= 1.22.0 < 1.26.1 | 1.26.1 |
| openshift | ose-rhel-coreos-8 | — | — |
| openshift | ose-rhel-coreos-9 | — | — |
CVSS provenance
nvdv3.16.5MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:L
vendor_redhat6.5MEDIUM
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Red Hat
unbound: Unbound: Denial of Service via use-after-free in DoQ stream output buffer
vendor_redhat·2026-09-16·CVSS 6.5
CVE-2026-78227 [MEDIUM] CWE-825 unbound: Unbound: Denial of Service via use-after-free in DoQ stream output buffer
unbound: Unbound: Denial of Service via use-after-free in DoQ stream output buffer
A flaw was found in Unbound. This vulnerability occurs in the DNS-over-QUIC (DoQ) stream output buffer when a client sends a RESET_STREAM, causing the output buffer to be freed while retransmission entries still point to it. A remote attacker, by querying Unbound over DoQ, withholding acknowledgments, and sending a RESET_STREAM, can trigger this flaw. This leads to retransmissions against freed memory, ultimately resulting in a denial of service due to an abnormal server exit.
Package: openshift/ose-rhel-coreos-8 (Red Hat OpenShift Container Platform 4) - Fix deferred
Package: openshift/ose-rhel-coreos-9 (Red Hat OpenShift Container Platform 4) - Fix deferred
GHSA
NLnet Labs Unbound 1.22.0 up to and including 1.26.1, has a use-after-free vulnerability when compiled for DNS-over-QUIC support with '--with-libngtcp2'.
ghsa_unreviewed·2026-09-16
CVE-2026-78227 [MEDIUM] CWE-416 NLnet Labs Unbound 1.22.0 up to and including 1.26.1, has a use-after-free vulnerability when compiled for DNS-over-QUIC support with '--with-libngtcp2'.
NLnet Labs Unbound 1.22.0 up to and including 1.26.1, has a use-after-free vulnerability when compiled for DNS-over-QUIC support with '--with-libngtcp2'. Each DoQ stream owns an output buffer that holds the DNS response. ngtcp2's retransmission buffer keeps a shallow pointer into the output buffer for as long as a STREAM frame may be resent. On a client RESET_STREAM, the output buffer is freed but ngtcp2 still holds the matching retransmission entries. The next PTO timeout makes ngtcp2 re-encode the STREAM frame and copy from the freed buffer. A malicious actor that can query Unbound over DoQ and that withholds ACKs, sends RESET_STREAM, and waits for PTO, reaches this use-after-free with no privilege. This leads to retransmissions against freed memory and eventually an abnormal server exit
No detection rules found.
No public exploits indexed.
Bugzilla
CVE-2026-78227 unbound: Unbound: Denial of Service via use-after-free in DoQ stream output buffer [fedora-all]
bugzilla·2026-09-21·CVSS 6.5
CVE-2026-78227 [MEDIUM] CVE-2026-78227 unbound: Unbound: Denial of Service via use-after-free in DoQ stream output buffer [fedora-all]
CVE-2026-78227 unbound: Unbound: Denial of Service via use-after-free in DoQ stream output buffer [fedora-all]
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
NLnet Labs Unbound 1.22.0 up to and including 1.26.1, has a use-after-free vulnerability when compiled for DNS-over-QUIC support with '--with-libngtcp2'. Each DoQ stream owns an output buffer that holds the DNS response. ngtcp2's retransmission buffer keeps a shallow pointer into the output buffer for as long as a STREAM frame may be resent. On a client RESET_STREAM, the output buffer is freed but ngtcp2 still holds the matching retransmission entries. The ne
Bugzilla
CVE-2026-78227 unbound: Unbound: Denial of Service via use-after-free in DoQ stream output buffer
bugzilla·2026-09-16·CVSS 6.5
CVE-2026-78227 [MEDIUM] CVE-2026-78227 unbound: Unbound: Denial of Service via use-after-free in DoQ stream output buffer
CVE-2026-78227 unbound: Unbound: Denial of Service via use-after-free in DoQ stream output buffer
NLnet Labs Unbound 1.22.0 up to and including 1.26.1, has a use-after-free vulnerability when compiled for DNS-over-QUIC support with '--with-libngtcp2'. Each DoQ stream owns an output buffer that holds the DNS response. ngtcp2's retransmission buffer keeps a shallow pointer into the output buffer for as long as a STREAM frame may be resent. On a client RESET_STREAM, the output buffer is freed but ngtcp2 still holds the matching retransmission entries. The next PTO timeout makes ngtcp2 re-encode the STREAM frame and copy from the freed buffer. A malicious actor that can query Unbound over DoQ and that withholds ACKs, sends RESET_STREAM, and waits for PTO, reaches this use-after-free with no p
Hackernews
Critical Unbound DNSSEC Validator Flaw Could Allow RCE via a Malicious DNS Zone
blogs_hackernews·2026-09-17·CVSS 9.8
CVE-2026-81642 [CRITICAL] Critical Unbound DNSSEC Validator Flaw Could Allow RCE via a Malicious DNS Zone
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## Critical Unbound DNSSEC Validator Flaw Could Allow RCE via a Malicious DNS Zone
Every release of the Unbound DNS resolver before 1.26.1 has a critical heap overflow in its DNSSEC validator, maintainer NLnet Labs said in an advisory on Wednesday.
An attacker who controls a malicious zone and queries a vulnerable resolver can trigger it, enabling remote code execution.
Unbound 1.26.1, released the same day, fixes the bug, tracked as CVE-2026-81642 , along with eight other flaws. One of the eight, CVE-2026-82717 , is a heap corruption bug in CNAME synthesis reported by Ben Morris of Anthropic. It could also lead to remote code
2026-09-16
Published