CVE-2023-1973

What it actually does

Crafted requests to FormAuthenticationMechanism trigger unbounded memory allocation leading to OutOfMemoryError and server process termination.

Why it matters to the business

Applications using the affected Undertow version can experience unplanned downtime and loss of service availability until the server is restarted or memory is recovered.

How an attack unfolds

An unauthenticated attacker repeatedly submits specially formatted authentication requests that cause the FormAuthenticationMechanism to allocate excessive memory objects; continued requests exhaust heap space and force an OutOfMemoryError that crashes the Undertow listener.

How to fix it

Upgrade Undertow on Debian 13 to version 2.3.18-1 or newer; after upgrade, restart all services that embed the library and verify the new version is loaded.

How to confirm the fix worked

Query the installed package version with apt-cache policy undertow or equivalent; confirm the running JAR or module reports version 2.3.18 or later; optionally replay a minimal crafted request in a test environment and verify no OOM occurs.

Typical attack path

1. Scan for publicly reachable Undertow endpoints exposing form-based login
2. Send repeated HTTP POST requests with crafted parameters targeting FormAuthenticationMechanism
3. Monitor server memory consumption until heap exhaustion occurs and the listener stops responding

How to detect it

Review web server access logs for unusually high volumes of POST requests to authentication endpoints; correlate with JVM heap or process memory metrics that show sustained growth without corresponding traffic increase.

What your security team should do

• Apply the 2.3.18-1 package update on all Debian 13 systems within the next maintenance window
• Add Undertow version checks to continuous compliance scans
• Monitor heap usage and request rates on authentication endpoints until patches are deployed