h2o quicly CRYPTO Stream assertion

CVSS Meta Temp Score
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CTI Interest Score
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5.3$0-$5k2.89

Summaryinfo

A vulnerability was found in h2o quicly and classified as problematic. This affects an unknown function of the component CRYPTO Stream. Executing a manipulation can lead to assertion. The identification of this vulnerability is CVE-2026-44435. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability classified as problematic was found in h2o quicly (the affected version is unknown). This vulnerability affects an unknown code of the component CRYPTO Stream. The manipulation with an unknown input leads to a assertion vulnerability. The CWE definition for the vulnerability is CWE-617. The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary. As an impact it is known to affect availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-44435 since 05/06/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are neither technical details nor an exploit publicly available.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Vendor

Name

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.3
VulDB Meta Temp Score: 5.3

VulDB Base Score: 5.3
VulDB Temp Score: 5.3
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Assertion
CWE: CWE-617
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: no mitigation known
Status: 🔍

0-Day Time: 🔒

Timelineinfo

05/06/2026 CVE reserved
07/16/2026 +71 days VulDB entry created
07/17/2026 +0 days Advisory disclosed
07/17/2026 +0 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: github.com
Status: Not defined

CVE: CVE-2026-44435 (🔒)
GCVE (CVE): GCVE-0-2026-44435
GCVE (VulDB): GCVE-100-379684

Entryinfo

Created: 07/17/2026 01:00
Changes: 07/17/2026 01:00 (51)
Complete: 🔍
Cache ID: 216::103

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