CVE-2026-74878 in openssl_encrypt
Summary
by MITRE • 08/17/2026
openssl_encrypt versions before 1.4.0 use an in-memory rate limiter for TOTP brute-force protection that is not shared across workers and is lost on server restart. Attackers can distribute authentication attempts across multiple server instances or retry immediately after a restart to bypass rate limiting protections.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 08/17/2026
The vulnerability identified in openssl_encrypt versions prior to 1.4.0 represents a critical flaw in the implementation of time-based one-time password (TOTP) brute-force protection mechanisms. The core issue stems from the use of an in-memory rate limiter designed to restrict the frequency of authentication attempts, thereby mitigating automated guessing attacks against user credentials. This security control is intended to enforce delays or blocks after a certain number of failed login attempts within a specific time window, which is a standard defense-in-depth strategy for preventing credential stuffing and brute-force attacks on multi-factor authentication systems.
However, the implementation relies exclusively on local server memory to track these rate limits rather than utilizing a centralized, distributed state management system such as Redis or a database-backed session store. Because the counter data resides in the volatile memory of individual application worker processes, it is inherently ephemeral and not synchronized across multiple instances of the service running behind a load balancer or within a containerized environment like Kubernetes. This architectural decision creates significant gaps in security coverage that can be systematically exploited by an attacker with knowledge of the system's deployment topology.
An adversary can bypass these protections through two primary vectors related to this distributed architecture flaw. First, if multiple server instances are handling authentication requests simultaneously, an attacker can distribute their brute-force attempts across different IP addresses or sessions targeting distinct worker nodes. Since each node maintains its own independent rate limit counter, the total number of allowed attempts is effectively multiplied by the number of active workers, allowing the attacker to exhaustively guess TOTP codes without triggering a block on any single instance. Second, because the state is stored in memory and not persisted, restarting the server or application process clears all existing counters. An attacker can monitor for service restarts or simply retry authentication attempts immediately after a deployment or crash occurs, effectively resetting the rate limiting window to zero and gaining unlimited free guesses before the system re-establishes any meaningful throttling thresholds.
From an industry standard perspective, this vulnerability aligns with CWE-384, which describes Session Fixation in the context of session state management, although more accurately it reflects CWE-798, Use of Hard-coded Credentials or Weak Authentication Mechanisms when considering the bypass of intended security controls due to improper implementation. In terms of offensive tactics, this flaw facilitates techniques associated with MITRE ATT&CK ID T1110, specifically Brute Force attacks, by removing the friction that rate limiting is designed to introduce. It also touches upon CWE-697 regarding Incorrect Comparison, as the system fails to correctly evaluate the global context of authentication attempts against a unified security policy.
The operational impact of this vulnerability is severe for any application relying on TOTP for two-factor or multi-factor authentication. Successful exploitation allows attackers to gain unauthorized access to user accounts without detection by automated defense systems. This can lead to data breaches, financial loss if payment credentials are compromised, and reputational damage due to the failure of a critical security control. The risk is particularly acute in high-traffic environments where horizontal scaling increases the number of worker nodes, thereby exponentially increasing the attack surface for distributed brute-force campaigns.
To mitigate this vulnerability, organizations must upgrade openssl_encrypt to version 1.4.0 or later, which presumably addresses these architectural deficiencies by implementing a shared state mechanism for rate limiting. In the interim, if upgrading is not immediately feasible, administrators should implement externalized session storage using technologies like Redis or Memcached that support distributed counters across all application instances. Additionally, integrating Web Application Firewalls (WAFs) with IP-based throttling rules can provide an additional layer of protection at the network perimeter, ensuring that rate limits are enforced regardless of which backend server handles a specific request. Monitoring for unusual spikes in authentication failures from diverse source IPs should also be prioritized to detect ongoing exploitation attempts.