CVE-2026-109786
Description
A flaw was found in fail2ban. The OpenSSH service filter improperly parses log entries when identifying offending network addresses. A remote, unauthenticated attacker can supply a crafted username during login attempts, causing the service to associate failed authentication events with an arbitrary source IP address. Consequently, this flaw can lead to the automated banning of legitimate users or systems, resulting in a Denial of Service (DoS).
Statement
Red Hat Product Security has determined that this vulnerability does not affect any currently supported Red Hat product. This assessment may evolve based on further analysis and discovery. For more information about this vulnerability and the products it affects, please see the linked references.
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
The regexp could accept substrings that match the pattern, which produces a partial comparison to the target. In some cases, this can allow dangerous substrings to bypass the intended protection.
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