GHSA-95h4-w6j8-2rp8 CVE-2025-9784

Undertow MadeYouReset HTTP/2 DDoS Vulnerability

High Maven

Severity: 7.5 / 10; High · CVSS 3.1
Exploit chance (EPSS): 2.33%; Chance of exploitation in the next 30 days. Higher than 83.50% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-404 Improper Resource Shutdown or Release; CWE-770 Allocation of Resources Without Limits or Throttling
Fix: 2.2.38.Final; Upgrade io.undertow:undertow-core to this version or later

Description

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).

Affected versions

Maven

Package	Vulnerable	Fixed in
io.undertow:undertow-core	`< 2.2.38.Final`	`2.2.38.Final`
io.undertow:undertow-core	`>= 2.3.0.Alpha1, < 2.3.20.Final`	`2.3.20.Final`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

io.undertow:undertow-core Maven → `2.2.38.Final`

maven

<dependency><groupId>io.undertow</groupId><artifactId>undertow-core</artifactId><version>2.2.38.Final</version></dependency>

gradle

implementation("io.undertow:undertow-core:2.2.38.Final")

Severity breakdown

CVSS 3.1 7.5

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Weakness

CWE-404: Improper Resource Shutdown or Release

The product does not release or incorrectly releases a resource before it is made available for re-use.

How to prevent it

Requirements: Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, languages such as Java, Ruby, and Lisp perform automatic garbage collection that releases memory for objects that have been deallocated.
Implementation: It is good practice to be responsible for freeing all resources you allocate and to be consistent with how and where you free memory in a function. If you allocate memory that you intend to free upon completion of the function, you must be sure to free the memory at all exit points for that function including error conditions.
Implementation: Memory should be allocated/freed using matching functions such as malloc/free, new/delete, and new[]/delete[].
Implementation: When releasing a complex object or structure, ensure that you properly dispose of all of its member components, not just the object itself.

CWE-770: Allocation of Resources Without Limits or Throttling

The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.

How to prevent it

Requirements: Clearly specify the minimum and maximum expectations for capabilities, and dictate which behaviors are acceptable when resource allocation reaches limits.
Architecture and Design: Limit the amount of resources that are accessible to unprivileged users. Set per-user limits for resources. Allow the system administrator to define these limits. Be careful to avoid CWE-410.
Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place, and it will help the administrator to identify who is committing the abuse. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, typically by using increasing time delays uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution can be difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply requires more resources on the part of the attacker.
Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
Architecture and Design, Implementation: If the program must fail, ensure that it fails gracefully (fails closed). There may be a temptation to simply let the program fail poorly in cases such as low memory conditions, but an attacker may be able to assert control before the software has fully exited. Alternately, an uncontrolled failure could cause cascading problems with other downstream components; for example, the program could send a signal to a downstream process so the process immediately knows that a problem has occurred and has a better chance of recovery. Ensure that all failures in resource allocation place the system into a safe posture.
Operation, Architecture and Design: Use quotas or other resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems. When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged users; alternately, begin releasing resources for less-privileged users. While this mitigation may protect the system from attack, it will not necessarily stop attackers from adversely impacting other users. Ensure that the application performs the appropriate error checks and error handling in case resources become unavailable (CWE-703).

References

Advisories

nvd.nist.gov/vuln/detail/CVE-2025-9784

Packages

github.com/undertow-io/undertow

Timeline

Sep 2, 2025 Published
Oct 14, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-3x3v-w654-m28m Undertow: Denial of Service via Multipart/Form-Data Parsing on HTTP GET Requests	Medium	Also affects io.undertow:undertow-core
GHSA-33hj-rcmx-86mv Undertow Servlets Vulnerable to Remote DoS via OutOfMemoryError when Passed Large Parameter Names	High	Also affects io.undertow:undertow-core
GHSA-j382-5jj3-vw4j Undertow HTTP server core doesn't properly validate the Host header in incoming HTTP requests	Critical	Also affects io.undertow:undertow-core
GHSA-6h4f-pj3g-q8fq Undertow OutOfMemory when parsing form data encoding with application/x-www-form-urlencoded	High	Also affects io.undertow:undertow-core
GHSA-3jrv-jgp8-45v3 Undertow incorrectly parses cookies	High	Also affects io.undertow:undertow-core
GHSA-97cq-f4jm-mv8h Undertow Denial of Service vulnerability	High	Also affects io.undertow:undertow-core
GHSA-9623-mqmm-5rcf Undertow vulnerable to Race Condition	High	Also affects io.undertow:undertow-core
GHSA-ch7q-gpff-h9hp Undertow Missing Release of Memory after Effective Lifetime vulnerability	Medium	Also affects io.undertow:undertow-core

Is this in your code?

MergeHarbor checks every repository's dependencies against this database, ranks what matters by exploitability and reachability, routes it to the owning team and opens the fix pull request.

Check your repos with MergeHarbor