CVE-2026-73493
http4s-blaze-server: Unbounded WebSocket message aggregation
Description
Http4s (http4s-blaze-server) is a minimal, idiomatic Scala interface for HTTP services. Prior to 0.23.18 and 1.0.0-M42, http4s-blaze-server aggregates fragments of an incoming WebSocket message with no limit on total size or fragment count. A client that completes a WebSocket handshake can send an unterminated fragmented message and drive unbounded heap growth in the server JVM, resulting in denial of service through OutOfMemoryError. Any http4s application serving WebSocket routes over BlazeServerBuilder is affected, no non-default configuration is required, and maxWebSocketBufferSize does not bound the aggregate because it bounds only individual frames. A single connection sending continuation frames that never set FIN forces the server to buffer every fragment until the heap is exhausted, terminating the JVM with OutOfMemoryError on the blaze selector thread. Small fragments amplify the cost through per-frame object overhead, so a modest volume of wire bytes is sufficient. This issue is fixed in versions 0.23.18 and 1.0.0-M42.
INFO
Published Date :
Aug. 12, 2026, 10:17 p.m.
Last Modified :
Oct. 24, 2026, 3:10 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 | HIGH | [email protected] | ||||
| CVSS 3.1 | HIGH | MITRE-CVE |
Solution
- Update http4s-blaze-server to version 0.23.18 or later.
- Update http4s-blaze-server to version 1.0.0-M42 or later.
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-2026-73493.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-73493 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-2026-73493
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-2026-73493 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-73493 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.
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CVE Translated by [email protected]
Oct. 24, 2026
Action Type Old Value New Value Changed Translation Title: blaze de http4s, Description: Http4s (http4s-blaze-server) es una interfaz Scala mínima e idiomática para servicios HTTP. Antes de 0.23.18 y 1.0.0-M42, http4s-blaze-server agrega fragmentos de un mensaje WebSocket entrante sin límite en el tamaño total o el recuento de fragmentos. Un cliente que completa un handshake WebSocket puede enviar un mensaje fragmentado no terminado y provocar un crecimiento ilimitado del heap en la JVM del servidor, lo que resulta en una denegación de servicio a través de OutOfMemoryError. Cualquier aplicación http4s que sirva rutas WebSocket sobre BlazeServerBuilder se ve afectada, no se requiere ninguna configuración no predeterminada, y maxWebSocketBufferSize no limita el agregado porque solo limita los frames individuales. Una única conexión que envía frames de continuación que nunca establecen FIN fuerza al servidor a almacenar en búfer cada fragmento hasta que el heap se agota, terminando la JVM con OutOfMemoryError en el hilo selector de blaze. Los fragmentos pequeños amplifican el costo a través de la sobrecarga de objetos por frame, por lo que un volumen modesto de bytes en la red es suficiente. Este problema está solucionado en las versiones 0.23.18 y 1.0.0-M42. Title: blaze de http4s, Description: Http4s (http4s-blaze-server) es una interfaz Scala mínima e idiomática para servicios HTTP. Antes de 0.23.18 y 1.0.0-M42, http4s-blaze-server agrega fragmentos de un mensaje WebSocket entrante sin límite en el tamaño total o el recuento de fragmentos. Un cliente que completa un handshake WebSocket puede enviar un mensaje fragmentado no terminado y provocar un crecimiento ilimitado del heap en la JVM del servidor, lo que resulta en una denegación de servicio a través de OutOfMemoryError. Cualquier aplicación http4s que sirva rutas WebSocket sobre BlazeServerBuilder se ve afectada, no se requiere ninguna configuración no predeterminada, y maxWebSocketBufferSize no limita el agregado porque solo limita los frames individuales. Una única conexión que envía frames de continuación que nunca establecen FIN fuerza al servidor a almacenar en búfer cada fragmento hasta que el heap se agota, terminando la JVM con OutOfMemoryError en el hilo selector de blaze. Los fragmentos pequeños amplifican el costo a través de la sobrecarga de objetos por frame, por lo que un volumen modesto de bytes en la red es suficiente. Este problema está solucionado en las versiones 0.23.18 y 1.0.0-M42. -
CVE Translated by [email protected]
Oct. 23, 2026
Action Type Old Value New Value Added Translation Title: blaze de http4s, Description: Http4s (http4s-blaze-server) es una interfaz Scala mínima e idiomática para servicios HTTP. Antes de 0.23.18 y 1.0.0-M42, http4s-blaze-server agrega fragmentos de un mensaje WebSocket entrante sin límite en el tamaño total o el recuento de fragmentos. Un cliente que completa un handshake WebSocket puede enviar un mensaje fragmentado no terminado y provocar un crecimiento ilimitado del heap en la JVM del servidor, lo que resulta en una denegación de servicio a través de OutOfMemoryError. Cualquier aplicación http4s que sirva rutas WebSocket sobre BlazeServerBuilder se ve afectada, no se requiere ninguna configuración no predeterminada, y maxWebSocketBufferSize no limita el agregado porque solo limita los frames individuales. Una única conexión que envía frames de continuación que nunca establecen FIN fuerza al servidor a almacenar en búfer cada fragmento hasta que el heap se agota, terminando la JVM con OutOfMemoryError en el hilo selector de blaze. Los fragmentos pequeños amplifican el costo a través de la sobrecarga de objetos por frame, por lo que un volumen modesto de bytes en la red es suficiente. Este problema está solucionado en las versiones 0.23.18 y 1.0.0-M42. -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Aug. 13, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-73493', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-08-13T17:49:17.058412Z'} -
New CVE Received by [email protected]
Aug. 12, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'http4s', 'product': 'blaze', 'versions': [{'status': 'affected', 'version': '< 0.23.18'}, {'status': 'affected', 'version': '>= 1.0.0-M1, < 1.0.0-M42'}]}] Added Description Http4s (http4s-blaze-server) is a minimal, idiomatic Scala interface for HTTP services. Prior to 0.23.18 and 1.0.0-M42, http4s-blaze-server aggregates fragments of an incoming WebSocket message with no limit on total size or fragment count. A client that completes a WebSocket handshake can send an unterminated fragmented message and drive unbounded heap growth in the server JVM, resulting in denial of service through OutOfMemoryError. Any http4s application serving WebSocket routes over BlazeServerBuilder is affected, no non-default configuration is required, and maxWebSocketBufferSize does not bound the aggregate because it bounds only individual frames. A single connection sending continuation frames that never set FIN forces the server to buffer every fragment until the heap is exhausted, terminating the JVM with OutOfMemoryError on the blaze selector thread. Small fragments amplify the cost through per-frame object overhead, so a modest volume of wire bytes is sufficient. This issue is fixed in versions 0.23.18 and 1.0.0-M42. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Added CWE CWE-770 Added Reference https://github.com/http4s/blaze/commit/173e8ca820a0d12110bfe409c72e9b9c3d28d471 Added Reference https://github.com/http4s/blaze/releases/tag/v0.23.18 Added Reference https://github.com/http4s/blaze/releases/tag/v1.0.0-M42 Added Reference https://github.com/http4s/blaze/security/advisories/GHSA-7ppr-r889-mcf2