CVE-2026-78594 in APM Server
Summary
by MITRE • 09/02/2026
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.
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Analysis
by VulDB Data Team • 09/02/2026
The vulnerability identified as CWE-409 represents a critical failure in input validation and resource management within the Application Performance Monitoring server component of Elastic Stack products. This flaw specifically affects how the APM Server handles data that has been subjected to high levels of compression, such as gzip or deflate encoded payloads. The core technical deficiency lies in the absence of strict limits on decompressed payload sizes during ingestion. When a user submits content for storage, particularly source map files used for debugging JavaScript errors, the server attempts to decompress the incoming stream without adequately verifying whether the resulting uncompressed data will exceed available system memory resources. This lack of pre-processing validation allows an attacker to craft a small compressed file that expands into a massive amount of data upon decomposition, effectively bypassing standard size checks applied to raw input streams.
The operational impact of this vulnerability is severe and persistent, leading directly to a denial of service condition through excessive resource allocation. An authenticated user possessing write access to source map content can exploit this flaw by uploading specially crafted compressed files designed to consume nearly all available memory on the host machine when processed. As the APM Server attempts to decompress and store these payloads, it triggers an out-of-memory state that causes the application process to crash or terminate abruptly due to insufficient heap space. Unlike transient crashes caused by single malformed requests, this vulnerability creates a persistent threat because the malicious content is stored in the system's data storage before processing occurs. Consequently, every time the APM Server restarts and attempts to load or index these stored source maps, it will repeatedly exhaust memory resources, leading to continuous service disruption until the offending files are manually identified and removed from the backend storage.
From a threat modeling perspective, this vulnerability aligns with CAPEC-130, which describes attacks involving excessive allocation of system resources. The attacker leverages the discrepancy between compressed input size and decompressed output volume to force the target application into an unsustainable resource state. This is distinct from traditional buffer overflow exploits as it targets memory management logic rather than code execution boundaries. Furthermore, this flaw relates closely to CWE-787, which covers out-of-bounds writes, although in this specific context, the primary consequence is service termination via exhaustion rather than arbitrary code execution or data corruption. The persistence of the issue highlights a significant gap in lifecycle management for stored artifacts within monitoring agents, where validation occurs at ingestion but not necessarily during retrieval and re-processing phases.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. Administrators should immediately audit source map storage locations to identify and delete any suspiciously large or recently uploaded compressed files that could trigger the memory exhaustion condition. To prevent recurrence, Elastic has released patches in versions 7.15.2, 8.0.1, and later releases of APM Server which implement stricter limits on decompressed payload sizes. Organizations running unpatched instances should apply these updates as a priority to restore service stability. Additionally, implementing network-level rate limiting or request size restrictions at the reverse proxy level can provide an additional layer of defense by blocking excessively large compressed uploads before they reach the application logic. Future development efforts should focus on enforcing strict decompression depth limits and validating uncompressed sizes against configured memory thresholds prior to allocation, ensuring that resource consumption remains predictable regardless of input compression ratios.