CVE-2025-59089 Python-kdcproxy: remote dos via unbounded tcp upstream buffering
An attacker can exhaust server memory and CPU resources by sending unbounded data to the Kerberos proxy, causing a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-59089?
CVE-2025-59089 is a medium-severity denial of service vulnerability in Red Hat Enterprise Linux 10, published on 12 Nov 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
If an attacker causes kdcproxy to connect to an attacker-controlled KDC server (e.g. through server-side request forgery), they can exploit the fact that kdcproxy does not enforce bounds on TCP response length to conduct a denial-of-service attack. While receiving the KDC's response, kdcproxy copies the entire buffered stream into a new buffer on each recv() call, even when the transfer is incomplete, causing excessive memory allocation and CPU usage. Additionally, kdcproxy accepts incoming response chunks as long as the received data length is not exactly equal to the length indicated in the response header, even when individual chunks or the total buffer exceed the maximum length of a Kerberos message. This allows an attacker to send unbounded data until the connection timeout is reached (approximately 12 seconds), exhausting server memory or CPU resources. Multiple concurrent requests can cause accept queue overflow, denying service to legitimate clients.
Weakness: CWE-770
Which versions are affected by CVE-2025-59089?
How do I fix CVE-2025-59089?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-59089 being exploited?
There is no known exploitation of CVE-2025-59089 in the wild and no public exploit code.
Sources
Also known as AZL-70171, AZL-70181, DEBIAN-CVE-2025-59089, GHSA-hxcg-77v3-qx52, UBUNTU-CVE-2025-59089.