CVE-2026-68762 in Ktor
Summary
by MITRE • 08/17/2026
In JetBrains Ktor before 3.4.1 potential DoS attack via WebSocket decompression was possible
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Analysis
by VulDB Data Team • 08/17/2026
The vulnerability identified in versions of the Kotlin Multiplatform Web framework, specifically Jetbrains Ktor prior to version 3.4.1, centers on a critical flaw within its WebSocket implementation regarding the handling of compression extensions. This issue allows for a Denial of Service attack vector that exploits the resource consumption inherent in decompression operations when processing maliciously crafted input data. The core technical deficiency lies in the lack of adequate bounds checking or rate limiting applied to the decompression process, which permits an attacker to trigger excessive memory allocation and CPU utilization by sending compressed payloads with high compression ratios or specifically designed malformed headers that force the server into a resource exhaustion state.
From a technical perspective, WebSocket connections often utilize extensions such as per-message-deflate to reduce bandwidth usage by compressing data before transmission. When Ktor receives these frames, it must decompress them to process the actual application payload. In vulnerable versions, the framework does not sufficiently validate the size of the uncompressed output relative to configured limits or available system resources. An attacker can exploit this by sending a small compressed packet that expands into an extremely large amount of data upon decompression. This technique, often referred to as a zip bomb attack in broader security contexts, forces the server's memory allocator to consume vast amounts of RAM rapidly. As multiple such connections are established or sustained, the cumulative effect leads to system instability, service crashes, or complete unavailability for legitimate users.
The operational impact of this vulnerability is severe, primarily affecting the availability component of the CIA triad. For organizations relying on Ktor for real-time communication services, chat applications, or live data streaming platforms, a successful exploitation can result in significant downtime and loss of service continuity. Beyond immediate disruption, repeated attacks may degrade system performance by consuming critical resources that should be allocated to legitimate traffic processing. This not only impacts user experience but also incurs potential financial losses due to operational interruptions and the need for emergency incident response efforts. The vulnerability is particularly dangerous because it can be executed remotely with minimal interaction from the attacker, requiring only a standard WebSocket connection initiation followed by the transmission of maliciously crafted frames.
In alignment with industry standards, this flaw maps directly to CWE-400, which describes uncontrolled resource consumption within a single entity or process. The attack methodology aligns with MITRE ATT&CK technique T1496, specifically Resource Hijacking via Denial of Service, where the adversary aims to exhaust system resources rather than compromise confidentiality or integrity. Mitigation strategies primarily involve upgrading to Ktor version 3.4.1 or later, which includes patches that enforce strict limits on decompressed data sizes and implement safeguards against excessive resource consumption during compression extension processing. Additionally, administrators should consider implementing network-level rate limiting for WebSocket connections and configuring application firewalls to detect and block anomalous traffic patterns indicative of such exploitation attempts until the software update is applied across all affected instances.