CVE-2026-24458 in Mattermost
Summary
by MITRE • 03/16/2026
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly handle very long passwords, which allows an attacker to overload the server CPU and memory via executing login attempts with multi-megabyte passwords. Mattermost Advisory ID: MMSA-2026-00587
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 03/20/2026
This vulnerability in Mattermost represents a critical resource exhaustion issue that stems from inadequate input validation during authentication processes. The flaw affects multiple version streams including 11.3.x through 11.3.0, 11.2.x through 11.2.2, and 10.11.x through 10.11.10, indicating a widespread vulnerability across the software's release lifecycle. The root cause lies in the system's failure to implement proper bounds checking on password length during login operations, creating a pathway for malicious actors to exploit server resources through carefully crafted authentication attempts.
The technical implementation of this vulnerability demonstrates a classic denial of service vector where attackers can submit extremely long passwords measured in megabytes rather than the typical password lengths users encounter. When the Mattermost server processes these oversized credentials, it attempts to hash and validate them using standard cryptographic functions, but the excessive input size causes disproportionate resource consumption. The server's memory allocation and CPU processing time increase exponentially with password length, creating a scenario where legitimate login attempts become impossible while the system becomes overwhelmed with processing demands.
From an operational perspective, this vulnerability presents significant risk to organizations relying on Mattermost for communication and collaboration services. The attack vector is relatively simple to execute since it only requires sending login requests with oversized passwords, making it an attractive target for attackers seeking to disrupt service availability. The impact extends beyond simple service disruption as the resource exhaustion can affect other system functions, potentially leading to cascading failures and extended downtime. Organizations may experience complete service unavailability during active exploitation attempts, with recovery requiring manual intervention and system restarts.
The vulnerability aligns with CWE-770, which addresses allocation of resources without limits or with inadequate limits, and maps to ATT&CK technique T1499.004 for network denial of service attacks. Security teams should implement immediate mitigations including rate limiting on authentication attempts, implementing maximum password length restrictions, and deploying intrusion detection systems to monitor for unusual login patterns. Organizations must also consider applying the vendor-provided patches as soon as they become available, while implementing temporary workarounds such as enforcing password complexity policies that naturally limit password length. The incident highlights the importance of robust input validation and resource management in authentication systems, emphasizing that even seemingly benign operations like password handling can become critical security concerns when not properly constrained.