CVE-2026-44433
Quicly is vulnerable to memory exhaustion
Description
Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server. Prior to commit 8b178e6, an adversarial peer could send a STREAM frame carrying just one byte at the largest offset being permitted to obtain additional flow control credit, which under certain circumstances could lead to a Denial of Service. Assuming the application prepares a receive buffer for storing all data that arrive out-of-order, up to the largest offset being received, this behavior could lead to the application allocating large amount of memory with the peer sending only a handful of packets, resulting in memory exhaustion. In addition to the receive buffer allocation strategy, the severity of this vulnerability depends on how the application controls the stream concurrency. In case of the H2O HTTP server, under its default setting, this bug increases the maximum amount of memory allocated per connection by about 4 times. This issue has been fixed by commit 8b178e6.
INFO
Published Date :
July 16, 2026, 11:16 p.m.
Last Modified :
Oct. 24, 2026, 8:10 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 3.1 | HIGH | [email protected] |
Solution
- Update Quicly to incorporate commit 8b178e6.
- Review and adjust memory allocation strategies.
- Configure stream concurrency limits.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-44433.
| URL | Resource |
|---|---|
| https://github.com/h2o/quicly/commit/8b178e692c51a3b1031612ef89f03a53aac63c15 | Patch |
| https://github.com/h2o/quicly/security/advisories/GHSA-f7qr-4p37-9gx9 | Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-44433 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-44433
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-44433 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-44433 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Translated by [email protected]
Oct. 24, 2026
Action Type Old Value New Value Added Translation Title: quicly de h2o, Description: Quicly es una implementación del protocolo IETF QUIC destinada principalmente para su uso dentro del servidor HTTP H2O. Antes del commit 8b178e6, un par adversario podía enviar un frame STREAM que transportaba solo un byte en el mayor offset permitido para obtener crédito adicional de control de flujo, lo que bajo ciertas circunstancias podría llevar a una denegación de servicio. Asumiendo que la aplicación prepara un búfer de recepción para almacenar todos los datos que llegan fuera de orden, hasta el mayor offset recibido, este comportamiento podría llevar a que la aplicación asigne una gran cantidad de memoria con el par enviando solo un puñado de paquetes, resultando en agotamiento de memoria. Además de la estrategia de asignación del búfer de recepción, la gravedad de esta vulnerabilidad depende de cómo la aplicación controla la concurrencia de streams. En el caso del servidor HTTP H2O, bajo su configuración predeterminada, este error aumenta la cantidad máxima de memoria asignada por conexión en aproximadamente 4 veces. Este problema ha sido solucionado por el commit 8b178e6. -
Initial Analysis by [email protected]
Aug. 06, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Added CPE Configuration OR *cpe:2.3:a:h2o:quicly:*:*:*:*:*:*:*:* versions up to (excluding) 2026-05-29 Added Reference Type GitHub, Inc.: https://github.com/h2o/quicly/commit/8b178e692c51a3b1031612ef89f03a53aac63c15 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/h2o/quicly/security/advisories/GHSA-f7qr-4p37-9gx9 Types: Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-44433', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-17T15:26:30.321361Z'} -
New CVE Received by [email protected]
Jul. 16, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'h2o', 'product': 'quicly', 'versions': [{'status': 'affected', 'version': '< 8b178e6'}]}] Added Description Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server. Prior to commit 8b178e6, an adversarial peer could send a STREAM frame carrying just one byte at the largest offset being permitted to obtain additional flow control credit, which under certain circumstances could lead to a Denial of Service. Assuming the application prepares a receive buffer for storing all data that arrive out-of-order, up to the largest offset being received, this behavior could lead to the application allocating large amount of memory with the peer sending only a handful of packets, resulting in memory exhaustion. In addition to the receive buffer allocation strategy, the severity of this vulnerability depends on how the application controls the stream concurrency. In case of the H2O HTTP server, under its default setting, this bug increases the maximum amount of memory allocated per connection by about 4 times. This issue has been fixed by commit 8b178e6. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Added CWE CWE-400 Added CWE CWE-770 Added Reference https://github.com/h2o/quicly/commit/8b178e692c51a3b1031612ef89f03a53aac63c15 Added Reference https://github.com/h2o/quicly/security/advisories/GHSA-f7qr-4p37-9gx9