The vulnerability (CVE-2025-48448) in the Drupal Admin Audit Trail module (versions prior to 1.0.5) is an 'Allocation of Resources Without Limits or Throttling' issue. According to the Drupal security advisory (SA-CONTRIB-2025-068), this occurs when the 'Admin Audit Trail: User Authentication' submodule is enabled. The module fails to sufficiently limit large values before logging user authentication events (login, logout, password reset requests), leading to excessive resource allocation and a potential denial of service. Without access to the specific patch or source code changes, it's impossible to pinpoint the exact vulnerable functions. However, the vulnerability lies within the logging mechanism of the user authentication submodule. Functions responsible for handling and logging these authentication events would be the ones to examine. The fix in version 1.0.5 likely introduced input validation or truncation for the data being logged.

Confidence is low because I could not retrieve the commit information or source code to verify the exact functions involved. The analysis is based on the description of the vulnerability in the advisories.