CVE-2026-78227 Affecting unbound package, versions *


Severity

Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.27% (19th percentile)

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  • Snyk IDSNYK-DEBIAN12-UNBOUND-19872491
  • published17 Sept 2026
  • disclosed16 Sept 2026

Introduced: 16 Sep 2026

NewCVE-2026-78227  (opens in a new tab)

How to fix?

There is no fixed version for Debian:12 unbound.

NVD Description

Note: Versions mentioned in the description apply only to the upstream unbound package and not the unbound package as distributed by Debian. See How to fix? for Debian:12 relevant fixed versions and status.

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.

CVSS Base Scores

version 3.1