CVE-2026-108525 in bandit
Summary
by MITRE • 10/26/2026
Allocation of Resources Without Limits or Throttling vulnerability in the HTTP/2 implementation of mtrudel bandit allows an unauthenticated remote attacker to exhaust server memory via DATA frames sent past the advertised receive window. The attacker requests a response larger than the 65,535-byte initial window and withholds WINDOW_UPDATE, so the stream process blocks while sending and stops reading, then floods small DATA frames on that stream. Every frame is queued in the stream's mailbox until the BEAM node runs out of memory.
Bandit.HTTP2.Connection.handle_frame/3 in lib/bandit/http2/connection.ex forwards each DATA frame to the stream process without consulting the receive window, and Bandit.HTTP2.FlowControl.compute_recv_window/2 replenishes the window as data arrives rather than as it is consumed, and never answers a violation with FLOW_CONTROL_ERROR.
This issue affects bandit: from 0.3.1 before 1.14.0.
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Analysis
by VulDB Data Team • 10/26/2026
The vulnerability identified in Bandit's HTTP/2 implementation represents a critical failure in resource management, specifically categorized under CWE-770 as Allocation of Resources Without Limits or Throttling. This flaw allows an unauthenticated remote attacker to trigger a denial-of-service condition by exhausting the server's available memory. The attack vector exploits the fundamental mechanics of the HTTP/2 protocol, particularly how data frames are processed and buffered within stream processes. By sending DATA frames that exceed the advertised receive window size while deliberately withholding WINDOW_UPDATE acknowledgments, an attacker can force the server into a state where it accumulates excessive amounts of unprocessed data in memory queues rather than discarding or rejecting them as per standard protocol compliance.
The technical root cause lies in two specific implementation errors within Bandit's HTTP/2 connection and flow control logic. First, the function handle_frame forwards DATA frames to stream processes without validating whether they fall within the current receive window limits. This bypasses a critical security boundary that is designed to prevent clients from overwhelming servers with excessive data volumes. Second, the compute_recv_window function replenishes the receive window based on data arrival rather than actual consumption by the application layer. Furthermore, the implementation fails to send a FLOW_CONTROL_ERROR frame when violations occur, which means the server continues to accept and buffer invalid frames indefinitely. This combination ensures that every maliciously crafted DATA frame is queued in the stream's mailbox, leading to unbounded memory growth until the BEAM node crashes due to out-of-memory conditions.
From an operational impact perspective, this vulnerability enables a remote denial-of-service attack with minimal effort from the attacker. Since no authentication is required, any external actor can target vulnerable instances of Bandit running versions between 0.3.1 and 1.14.0. The resulting memory exhaustion disrupts service availability for all users connected to the affected server, effectively taking down web applications or APIs hosted on these systems. This aligns with ATT&CK technique T1498 Network Denial of Service, where an adversary aims to impair the availability of targeted services by consuming resources such as bandwidth, processing power, or memory. The lack of throttling mechanisms means that even a single client can generate sufficient traffic volume to compromise server stability over time.
To mitigate this vulnerability, immediate updates to Bandit are required for all affected versions. Upgrading to version 1.14.0 or later resolves the issue by correcting the flow control logic and ensuring proper validation of DATA frames against receive window limits. In environments where upgrading is not immediately feasible, network-level mitigations such as rate limiting on incoming HTTP/2 connections can help reduce exposure. Additionally, configuring web server reverse proxies to enforce strict connection timeouts and memory quotas may provide a layer of defense by terminating streams that exhibit abnormal buffering behavior. Organizations should also monitor for unusual spikes in memory usage associated with specific client IPs or stream IDs, which could indicate an ongoing exploitation attempt targeting this flaw.