Improper Handling of Highly Compressed Data in APM Server Leading to Persistent Denial of Service
Improper Handling of Highly Compressed Data (CWE-409) in APM Server can lead to a persistent denial of service via Excessive Allocation (CAPEC-130). An authenticated user with write access to source map content could store specially crafted, highly compressed content that exhausts the memory available to APM Server when it is later processed, terminating the process. The condition recurs on every restart until the stored content is removed.
Affected Versions:
- 8.x: All versions from 8.0.0 up to and including 8.19.19
- 9.x:
- All versions from 9.0.0 up to and including 9.4.4
- Version 9.5.0
Affected Configurations:
APM Server instances with Real User Monitoring (RUM) enabled and source map fetching configured. RUM is disabled by default; deployments that have not explicitly enabled this feature are not affected by this vulnerability.
Solutions and Mitigations:
The issue is resolved in APM Server versions 8.19.20, 9.4.5, and 9.5.1.
For Users that Cannot Upgrade:
On APM Server binary deployments, set apm-server.rum.source_mapping.enabled to false. This disables source map processing, which is the affected functionality, while leaving the rest of Real User Monitoring in place. This option is not available to Fleet-managed deployments.
Alternatively, disable Real User Monitoring entirely by setting apm-server.rum.enabled to false. Because RUM is disabled by default, deployments that have not enabled it require no action.
Indicators of Compromise (IOC)
No specific indicators of compromise have been identified for this vulnerability.
Severity: CVSSv3.1: Medium ( 4.9 ) - CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
CVE ID: CVE-2026-78594
Problem Type: CWE-409 - Improper Handling of Highly Compressed Data (Data Amplification)
Impact: CAPEC-130 - Excessive Allocation