Description

An issue was discovered in Nagios XI before 5.9.3. The is_insecure_login_authenticated function uses a insecure timing comparison that leads to an attacker being able to bruteforce the admin password, by measuring timing differences in the comparison.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "3.5",
  "pubDate": "2026-09-14T04:16:35.293Z",
  "pubdate": "2026-09-14T04:16:35.293Z",
  "executiveSummary": "This vulnerability involves a timing side-channel flaw within the Nagios XI authentication mechanism, specifically residing in the is_insecure_login_authenticated function.\nThe issue allows remote attackers to bypass password complexity through iterative timing analysis, effectively enabling brute-force attacks against administrative credentials.\nBy measuring the execution time required for the application to reject an authentication attempt, an attacker can incrementally determine the correct password character by character.\nThe flaw affects Nagios XI versions prior to 5.9.3, posing a significant risk to organizational infrastructure integrity by potentially granting unauthorized administrative access to the monitoring platform.\nSuccessful exploitation requires network connectivity to the authentication interface and the capability to perform high-resolution timing measurements to filter out network jitter and processing latency.\nThe primary risk implication is the unauthorized takeover of the monitoring server, which could lead to further exploitation of the monitored network environment.",
  "technicalDetails": "The root cause of this vulnerability is the implementation of a non-constant time comparison operator within the is_insecure_login_authenticated function. In cryptographic and authentication contexts, string comparisons must be performed in constant time to prevent leaking information about the expected input. The existing implementation utilizes a standard string comparison that terminates as soon as a character mismatch is detected.\nWhen a user submits authentication credentials, the application compares the provided input against the stored hash or expected value. Because the standard comparison function exits early upon encountering the first incorrect byte, the total execution time of the function is proportional to the number of correctly guessed leading characters in the password. This behavior creates a measurable timing side-channel.\nThe exploitation flow follows a systematic iterative approach: 1. The attacker initiates a series of authentication requests targeting the Nagios XI login endpoint. 2. For the first character position, the attacker sends a set of requests testing all possible ASCII characters. 3. The attacker collects high-resolution timing samples for each request and calculates the mean processing time, attempting to filter out noise caused by network latency. 4. The character that yields a statistically significant increase in processing time is identified as the likely correct character for that position. 5. The attacker repeats this process for each subsequent character in the string until the full password is reconstructed.\nBecause the vulnerability is located in the authentication logic, it is accessible via the network without requiring prior authentication or elevated privileges. The impact is significant as it negates the effectiveness of password complexity, allowing an attacker to derive the admin password without triggering traditional account lockout mechanisms based on failed login counters, provided the attacker can maintain sufficient precision in their timing measurements. The lack of constant-time comparison in is_insecure_login_authenticated effectively converts the authentication gate into an oracle, leaking information about the secret credentials through the temporal domain."
}