CVE-2026-73493
Published:August 12, 2026
Updated:August 31, 2026
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.
Affected Packages
https://github.com/http4s/blaze.git (GITHUB):
Affected version(s) >=v1.0.0-M33 <v1.0.0-M42Fix Suggestion:
Update to version v1.0.0-M42https://github.com/http4s/blaze.git (GITHUB):
Affected version(s) >=v0.14.0 <v0.23.18Fix Suggestion:
Update to version v0.23.18org.http4s:http4s-blaze-server_2.13 (JAVA):
Affected version(s) >=1.0.0-M2 <1.0.0-M42Fix Suggestion:
Update to version 1.0.0-M42org.http4s:http4s-blaze-server_2.12 (JAVA):
Affected version(s) >=0.10.0-M10 <0.23.18Fix Suggestion:
Update to version 0.23.18org.http4s:http4s-blaze-server_2.13 (JAVA):
Affected version(s) >=0.10.0-M10 <0.23.18Fix Suggestion:
Update to version 0.23.18org.http4s:http4s-blaze-server_3 (JAVA):
Affected version(s) >=1.0.0-M22 <1.0.0-M42Fix Suggestion:
Update to version 1.0.0-M42org.http4s:http4s-blaze-server_2.13 (JAVA):
Affected version(s) >=0.10.0-M10 <0.23.18Fix Suggestion:
Update to version 0.23.18org.http4s:http4s-blaze-server_2.12 (JAVA):
Affected version(s) >=0.10.0-M10 <0.23.18Fix Suggestion:
Update to version 0.23.18Related Resources (9)
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Contact UsCVSS v4
Base Score:
8.7
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
7.5
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Weakness Type (CWE)
Allocation of Resources Without Limits or Throttling
EPSS
Base Score:
0.35