Spring Kafka's retry topic infrastructure did not sufficiently validate user-controlled header values before acting on them. A producer could send a record with a crafted retry_topic-attempts header to supply an out-of-range attempt count and cause the retry topic router to misidentify where the message was in the retry sequence. Affected versions: Spring for Apache Kafka 4.0.0 through 4.0.5; 3.3.0 through 3.3.15; 3.2.0 through 3.2.13; 2.9.0 through 2.9.13; 2.8.0 through 2.8.11.