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Back to active CVEs
Medium · CVSS 6.5CVE-2026-78227

Use-after-free in DoQ stream output buffer on reset re-transmissionCVE-2026-78227

Answer in brief

CVE-2026-78227 records a Medium severity (CVSS 6.5) vulnerability in Use-after-free in DoQ stream output buffer on reset re-transmission. The current sources do not mark it as known exploited. The current feed maps NLnet Labs/Unbound (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 16, 2026Updated Sep 23, 2026Source checked Oct 31, 2026First seen by HOL Sep 16, 2026Material review Sep 23, 2026
Upstream Advisory

Key facts

Risk
Medium · CVSS 6.5
Exploitation
Not marked as known exploited
Affected software
2 mapped packages or products
Fix availability
Available

Why this deserves its current priority

CVSS is 6.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps NLnet Labs/Unbound (generic). Check affected ranges and fixed versions before updating.

Affected products and reported versions
ProductAffected versionsFixed versions
cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*Not reportedNot reported
Mapped affected packages and fixed versions
PackageAffected rangeFixed version
NLnet Labs/Unboundgeneric>=1.22.0 <1.26.11.26.1

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for NLnet Labs/Unbound.
  2. 2Review the reported fix. Source-reported solution: This issue is fixed starting with version 1.26.1

Evidence timeline and material changes

  1. Published upstream

    Sep 16, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Sep 23, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Sep 16, 2026

Sources and claim methodology

  • Source referencenlnetlabs.nl
Upstream source description

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.

Quoted source text, attributed separately from HOL analysis.

Record context

Vulnerability class
Memory Corruption
EPSS
Not reported
CWE IDs
CWE-416
Source
CVE List V5
Source checked
Oct 31, 2026
References
1 linked source
Open source record