CVE-2026-73493: CWE-770: Allocation of Resources Without Limits or Throttling in http4s blaze
Http4s blaze-server versions prior to 0.23.18 and 1.0.0-M42 are vulnerable to an unbounded resource allocation issue in WebSocket message handling. An attacker can send fragmented WebSocket messages without termination, causing the server to buffer fragments indefinitely and exhaust JVM heap memory. This leads to a denial of service via OutOfMemoryError on the blaze selector thread. The vulnerability affects any http4s application using BlazeServerBuilder for WebSocket routes with default configuration. The issue is fixed in versions 0.23.18 and 1.0.0-M42.
AI Analysis
Technical Summary
The vulnerability (CVE-2026-73493) in http4s-blaze-server arises from the aggregation of incoming WebSocket message fragments without limits on total size or fragment count. Clients completing a WebSocket handshake can send unterminated fragmented messages, forcing the server JVM to buffer fragments indefinitely. This unbounded buffering leads to heap exhaustion and JVM termination with OutOfMemoryError on the blaze selector thread. The maxWebSocketBufferSize setting only limits individual frame size, not the total aggregated message size, so it does not mitigate this issue. Small fragments increase the overhead, making even modest data volumes sufficient to trigger the condition. The flaw affects all versions before 0.23.18 and version 1.0.0-M42. The vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling).
Potential Impact
Successful exploitation results in denial of service by causing the server JVM to run out of heap memory and crash with an OutOfMemoryError. This disrupts availability of http4s applications serving WebSocket routes over BlazeServerBuilder. There is no impact on confidentiality or integrity reported. The vulnerability requires no privileges or user interaction beyond establishing a WebSocket connection.
Mitigation Recommendations
This vulnerability is fixed in http4s-blaze-server versions 0.23.18 and 1.0.0-M42. Users should upgrade to these or later versions to remediate the issue. No other configuration changes or mitigations are indicated. Patch status is not explicitly stated as 'official-fix' in the vendor advisory, but the fixed versions are clearly identified. No known exploits are reported in the wild.
CVE-2026-73493: CWE-770: Allocation of Resources Without Limits or Throttling in http4s blaze
Description
Http4s blaze-server versions prior to 0.23.18 and 1.0.0-M42 are vulnerable to an unbounded resource allocation issue in WebSocket message handling. An attacker can send fragmented WebSocket messages without termination, causing the server to buffer fragments indefinitely and exhaust JVM heap memory. This leads to a denial of service via OutOfMemoryError on the blaze selector thread. The vulnerability affects any http4s application using BlazeServerBuilder for WebSocket routes with default configuration. The issue is fixed in versions 0.23.18 and 1.0.0-M42.
CVSS v3.1
Score 7.5high
Affected software
pkg:github/http4s/blazeRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability (CVE-2026-73493) in http4s-blaze-server arises from the aggregation of incoming WebSocket message fragments without limits on total size or fragment count. Clients completing a WebSocket handshake can send unterminated fragmented messages, forcing the server JVM to buffer fragments indefinitely. This unbounded buffering leads to heap exhaustion and JVM termination with OutOfMemoryError on the blaze selector thread. The maxWebSocketBufferSize setting only limits individual frame size, not the total aggregated message size, so it does not mitigate this issue. Small fragments increase the overhead, making even modest data volumes sufficient to trigger the condition. The flaw affects all versions before 0.23.18 and version 1.0.0-M42. The vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling).
Potential Impact
Successful exploitation results in denial of service by causing the server JVM to run out of heap memory and crash with an OutOfMemoryError. This disrupts availability of http4s applications serving WebSocket routes over BlazeServerBuilder. There is no impact on confidentiality or integrity reported. The vulnerability requires no privileges or user interaction beyond establishing a WebSocket connection.
Mitigation Recommendations
This vulnerability is fixed in http4s-blaze-server versions 0.23.18 and 1.0.0-M42. Users should upgrade to these or later versions to remediate the issue. No other configuration changes or mitigations are indicated. Patch status is not explicitly stated as 'official-fix' in the vendor advisory, but the fixed versions are clearly identified. No known exploits are reported in the wild.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-08-12T19:00:33.735Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a7ce514bf8831d5392fb5e1
Added to database: 08/12/2026, 21:26:44 UTC
Last enriched: 08/12/2026, 21:41:31 UTC
Last updated: 08/12/2026, 21:41:31 UTC
Views: 5
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