CVE-2026-78227 (GCVE-0-2026-78227)

Vulnerability from cvelistv5 – Published: 2026-09-16 08:29 – Updated: 2026-09-16 15:33
VLAI
Title
Use-after-free in DoQ stream output buffer on reset re-transmission
Summary
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.
Severity
6.5 (Medium)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:L
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-16 15:33 UTC
CWE
Assigner
NLnet Labs CNA
CNA scorecard B 82/100 over 61 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
NLnet Labs Unbound Affected: 1.22.0 , < 1.26.1 (semver)
guessed Create a notification for this product.
Date Public
2026-09-16 00:00
Credits
Yuqi Qiu (Nankai University, AOSP Lab) Xiang Li (Nankai University, AOSP Lab)
Show details on NVD website
To clipboard 

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