CVE-2026-33013: Micronaut vulnerable to DoS via crafted form-urlencoded body binding with descending array indices
In JsonBeanPropertyBinder::expandArrayToThreshold in io.micronaut:micronaut-json-core before Micronaut 4 4.10.16 and in Micronaut 3 before 3.10.5 does not correctly handle descending array index order during form-urlencoded body binding, which allows remote attackers to cause a denial of service (non-terminating loop, CPU exhaustion, and OutOfMemoryError) via crafted indexed form parameters (e.g., authors[1].name followed by authors[0].name).
Example
With such an application
java package dosform;
import io.micronaut.http.HttpResponse; import io.micronaut.http.MediaType; import io.micronaut.http.annotation.Body; import io.micronaut.http.annotation.Consumes; import io.micronaut.http.annotation.Controller; import io.micronaut.http.annotation.Get; import io.micronaut.http.annotation.Post; import io.micronaut.http.annotation.Produces;
import java.net.URI;
@Controller class HomeController {
@Produces(MediaType.TEXTHTML) @Get String index() { return """ <!DOCTYPE html> <html> <head> <title></title> </head> <body> <form action="/submit" method="post"> <label for="firstAuthor">Fist Author</label> <input id="firstAuthor" name="authors[0].name" type="text"/>
<label for="secondAuthor">Second Author</label> <input id="secondAuthor" name="authors[1].name" type="text"/> <label for="thirdAuthor">Third Author</label> <input id="thirdAuthor" name="authors[2].name" type="text"/>
<button type="submit">Submit</button> </form> </body> </html> """; }
@Consumes(MediaType.APPLICATIONFORMURLENCODED) @Post("/submit") HttpResponse<?> submit(@Body Book book) { return HttpResponse.seeOther(URI.create("/")); } } package dosform;
import io.micronaut.core.annotation.Introspected;
import java.util.Objects;
@Introspected public class Author { private String name; public String getName() { return name; } public void setName(String name) { this.name = name; }
@Override public final boolean equals(Object o) { if (!(o instanceof Author)) return false;
Author author = (Author) o; return Objects.equals(name, author.name); }
@Override public int hashCode() { return Objects.hashCode(name); }
@Override public String toString() { return "Author{" + "name='" + name + '\'' + '}'; } } package dosform;
import io.micronaut.core.annotation.Introspected;
import java.util.List; import java.util.Objects;
@Introspected public class Book { private List<Author> authors; public List<Author> getAuthors() { return authors; } public void setAuthors(List<Author> authors) { this.authors = authors; }
@Override public final boolean equals(Object o) { if (!(o instanceof Book)) return false;
Book book = (Book) o; return Objects.equals(authors, book.authors); }
@Override public int hashCode() { return Objects.hashCode(authors); }
@Override public String toString() { return "Book{" + "authors=" + authors + '}'; } }
Sending curl -v -X POST 'http://127.0.0.1:8080/submit' -H 'Content-Type: application/x-www-form-urlencoded' --data-urlencode 'authors[1].name=RobertGalbraith' --data-urlencode 'authors[0].name=JKRowling' causes sustained CPU usage and unbounded memory growth (eventually OutOfMemoryError).
Patches For Micronaut 4, the problem has been patched in micronaut-core, dependencies with group id io.micronaut, since 4.10.16.
For Micronaut 3, the problem has been patched since 3.10.5
Users upgrade to the latest version of the framework.
Workarounds There is no way for users to fix or remediate the vulnerability without upgrading.
References PR Fix: https://github.com/micronaut-projects/micronaut-core/pull/12410
Other sources
Micronaut Framework is a JVM-based full stack Java framework designed for building modular, easily testable JVM applications. Versions prior to both 4.10.16 and 3.10.5 do not correctly handle descending array index order during form-urlencoded body binding in theJsonBeanPropertyBinder::expandArrayToThreshold, which allows remote attackers to cause a DoS (non-terminating loop, CPU exhaustion, and OutOfMemoryError) via crafted indexed form parameters (e.g., authors[1].name followed by authors[0].name). This issue has been fixed in versions 4.10.16 and 3.10.5.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-33013?
CVE-2026-33013 has a severity rating of high with a CVSS score of 8.2.
How do I fix CVE-2026-33013?
To fix CVE-2026-33013, you should apply the latest patch available for Micronaut according to the remediation guidance.
What type of vulnerability is CVE-2026-33013?
CVE-2026-33013 is a denial of service (DoS) vulnerability that affects the binding of form-urlencoded bodies.
Which versions of Micronaut are affected by CVE-2026-33013?
CVE-2026-33013 affects Micronaut versions before 4.10.16 and 3.x versions before 3.10.5.
What impact does CVE-2026-33013 have on applications?
CVE-2026-33013 can allow remote attackers to cause a denial of service, negatively impacting application availability.