CVE-2026-39804
Description
A flaw was found in bandit. An unauthenticated attacker who can open a WebSocket connection can exploit a vulnerability when WebSocket permessage-deflate compression is enabled. This flaw allows for memory exhaustion by sending a highly compressed frame that, when decompressed, forces large memory allocations. This can lead to a denial of service (DoS) by exhausting the system's memory and causing the application to crash.
Statement
This IMPORTANT DoS vulnerability in Bandit affects WebSocket connections with permessage-deflate compression enabled. Exploitation requires no authentication and is network-accessible. Impact is high availability loss through memory exhaustion. Stock Phoenix and LiveView applications are not affected as they default to compress: false. Affects Bandit versions 0.5.9 to before 1.11.0.
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Resource Consumption (Other)
When allocating resources without limits, an attacker could prevent other systems, applications, or processes from accessing the same type of resource. It can be easy for an attacker to consume many resources by rapidly making many requests or causing larger resources to be used than is needed.
Frequently Asked Questions
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