Python-kdcproxy: remote dos via unbounded tcp upstream buffering

Summary

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.

Timeline

1. Nov 12, 2025, 4:40 PM UTCCVE published
2. Nov 12, 2025, 8:47 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Jun 30, 2026, 3:11 AM UTCRecord last updated

Affected versions

• kdcproxy

  fixed in 1.1.0

• python-kdcproxy

  Version range not reported

• python-kdcproxy

  Version range not reported

• python-kdcproxy

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• idm:client

  Version range not reported

• idm:DL1

  Version range not reported

• idm:DL1

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• idm:DL1

  Version range not reported

• idm:DL1

  Version range not reported

• idm:DL1

  Version range not reported

• idm:DL1

  Version range not reported

• idm:DL1

  Version range not reported

• idm:DL1

  Version range not reported

• idm:DL1

  Version range not reported

• python-kdcproxy

  Version range not reported

• python-kdcproxy

  Version range not reported

• python-kdcproxy

  Version range not reported

• python-kdcproxy

  Version range not reported

• python-kdcproxy

  Version range not reported

References 17