Quicly: Remote Denial of Service via assertion failure when CRYPTO stream handshake data exceeds 32KB (CVE-2026-44435) | HOL Guard CVE

High · CVSS 7.5CVE-2026-44435

Quicly: Remote Denial of Service via assertion failure when CRYPTO stream handshake data exceeds 32KB

Answer in brief

CVE-2026-44435 records a High severity (CVSS 7.5) vulnerability in Quicly: Remote Denial of Service via assertion failure when CRYPTO stream handshake data exceeds 32KB. The current sources do not mark it as known exploited. The current feed maps h2o/quicly (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 Jul 16, 2026Updated Aug 6, 2026Source checked Sep 19, 2026First seen by HOL Jul 17, 2026Material review Aug 6, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.5
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Not reported

Why this deserves its current priority

CVSS is 7.5. 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 h2o/quicly (generic). Check affected ranges and fixed versions before updating.

Affected products and reported versions
Product	Affected versions	Fixed versions
cpe:2.3:a:h2o:quicly::::::::	Not reported	Not reported

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
h2o/quiclygeneric	< 937d0e9	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for h2o/quicly.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Jul 16, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 6, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Jul 17, 2026

Sources and claim methodology

Upstream source description

Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server. Prior to commit 937d0e9, an assertion failure is raised when the total number of valid handshake messages received over a CRYPTO stream of a single packet number space exceeds 32KB, causing a Denial of Service. This issue has been fixed by commit 937d0e9.

Quoted source text, attributed separately from HOL analysis.