A flaw was found in Undertow. A remote attacker could exploit this vulnerability by sending specially crafted WebSocket messages with permessage-deflate negotiated. This could lead to excessive memory consumption due to the PerMessageDeflateFunction.largerBuffer() method using exponential doubling, resulting in a Denial of Service (DoS) for the affected application.

A flaw was found in Undertow where malformed client requests can trigger server-side stream resets without triggering abuse counters. This issue, referred to as the "MadeYouReset" attack, allows malicious clients to induce excessive server workload by repeatedly causing server-side stream aborts. While not a protocol bug, this highlights a common implementation weakness that can be exploited to cause a denial of service (DoS).

A flaw was found in Undertow that can cause remote denial of service attacks. When the server uses the FormEncodedDataDefinition.doParse(StreamSourceChannel) method to parse large form data encoding with application/x-www-form-urlencoded, the method will cause an OutOfMemory issue. This flaw allows unauthorized users to cause a remote denial of service (DoS) attack.

Summary: Undertow’s PerMessageDeflateFunction.largerBuffer() uses exponential doubling

Requirements To Exploit: Any application using Undertow’s WebSocket with permessage-deflate is

affected. This includes:

WildFly application server (uses Undertow as its web layer)

Red Hat JBoss Enterprise Application Platform (JBoss EAP)

Any standalone Undertow WebSocket application using

PerMessageDeflateHandshake

The vulnerability requires only a standard WebSocket connection with

permessage-deflate negotiated, no authentication, no special configuration.

Component Affected: io.undertow:undertow-core

Version Affected: Undertow 2.3.18.Final

Patch Available: no

Version Fixed: N/A

Cvss: Score: 7.5 HIGH Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Impact: IMPORTANT

Steps To Reproduce: I have attached a self-contained Maven project (undertow-websocket-poc.tar.gz)

containing 6 tests:

Baselines:

Baseline 1a: Valid Origin -> upgrade accepted, message delivered

Baseline 1b: Invalid Origin -> HTTP 403 rejected

Mitigation: Add a maxDecompressedBufferSize parameter to PerMessageDeflateHandshake

(e.g. default 10 MB) that limits the largerBuffer() growth

Add a maximum doubling count or absolute buffer cap in largerBuffer()

Add a maxDecompressionRatio check (reject if wire:decompressed > 100x)

Add a maxFragmentsPerMessage limit in WebSocketChannel

Add Ping rate limiting in WebSocketChannel before generating Pong

Expose these limits in the PerMessageDeflateHandshake constructor

A flaw was found in Undertow. Servlets using a method that calls HttpServletRequestImpl.getParameterNames() can cause an OutOfMemoryError when the client sends a request with large parameter names. This issue can be exploited by an unauthorized user to cause a remote denial-of-service (DoS) attack.

A flaw was found in Undertow. A remote attacker can cause Out of Memory on websockets endpoint without authentication on any @ServerEndpoint class that has any @OnMessage method. This allows an attacker to cause Denial of Service attack without authentication and using only a standard WebSocket handshake.

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A vulnerability was found in Undertow. Undertow chunked response hangs after the body was flushed. The response headers and body were sent but the client would continue waiting as Undertow does not send the expected 0\r\n termination of the chunked response. This results in an uncontrolled resource consumption leaving the server side to a Denial of Service vulnerability attack. This happens only with Java 17 TLSv1.3 scenarios.

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There exists a security vulnerability in Undertow that can cause remote DoS attacks. When server uses method FormEncodedDataDefinition.doParse(StreamSourceChannel) to parse large form data encoding with application/x-www-form-urlencoded, the method will cause OutOfMemory. This vulnerability can be exploited by unauthorized users to cause remote denial-of-service (DoS) attack.

This happens because there is no size limit for this method hence a large request may jeopardize the environment leading to DoS.

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