External risk intelligence

openssl_encrypt TOTP Rate Limiter Bypass

CVE advisorySeverity: CRITICAL (CVSS 9.3)

CVE-2026-74878

The vulnerability affects a TOTP (Time-based One-Time Password) implementation, which is a mechanism explicitly designed for authentication. Authentication portals and identity services are inherently internet-facing, public-facing components of an application's architecture.

Halo Surface Signal: 5 out of 5 — more likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This advisory details a vulnerability in a time-based one-time password (TOTP) implementation that affects how authentication attempts are managed. The issue stems from an in-memory rate limiter that is not consistently applied across different server processes, allowing attackers to bypass protections by distributing attempts or retrying after a server restart. This could potentially weaken authentication security for systems relying on this specific TOTP mechanism.

Authentication protection can be bypassed.
Totp bypass could weaken security controls.
Confirm relevance and potential exposure.

Attack Path

How an attacker could exploit the issue

An attacker could target an application using a vulnerable version of openssl_encrypt to bypass its one-time password rate limiting. This could be achieved by distributing login attempts across multiple server instances or by immediately retrying after a server restart, as the rate limiter is not shared between workers and resets upon restart. Successful bypass could lead to brute-force attacks against authentication mechanisms.

No authentication or special access needed.
Bypass TOTP rate limiting by distributing or retrying.
Risk of brute-forcing authentication.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow attackers to bypass rate limiting protections for Time-based One-Time Password (TOTP) authentication. By distributing attempts across multiple server instances or retrying after a restart, attackers could circumvent safeguards designed to prevent brute-force attacks. This may affect the integrity of authentication mechanisms when supported by the advisory's context.

Authentication mechanisms at risk.
Bypassing rate limits across instances.
Increased risk of unauthorized access.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in TOTP rate limiting can be bypassed by distributing attempts across instances or after restarts, potentially impacting authentication services. The first step is to identify all deployments of this technology, confirm their exposure and business criticality, and then assign ownership for remediation.

App owners, platform teams to manage issues.
Verify TOTP service reachability and criticality.
Plan remediation, considering vendor coordination.

Supplementary metadata

CVSS vector

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Frequently asked questions

What is openssl_encrypt and where is it used?

The openssl_encrypt software is a library component used by developers to handle cryptographic operations within their applications. It is frequently integrated into authentication workflows, specifically providing Time-based One-Time Password (TOTP) functionality. Developers include it to secure login processes by requiring a second factor for user verification, relying on this library to validate and protect those temporary codes.

What does CVE-2026-74878 mean for authentication security?

This vulnerability is classified as CWE-770, which involves the allocation of resources without appropriate limits. In this case, the weakness lies in how the software manages rate limiting for authentication attempts. Because the limit is tracked only in the memory of individual server processes, it fails to act as a global barrier, allowing an attacker to ignore restrictions intended to stop automated, high-speed guessing of passwords.

How can an attacker trigger this rate limiter bypass?

An attacker exploits this by circumventing the protection mechanism rather than breaking the encryption itself. They can spread their guessing attempts across multiple server instances, ensuring no single instance triggers the limit. Additionally, because the rate-tracking data is stored in memory and disappears when a server restarts, triggering or waiting for a restart effectively wipes the attacker's history, allowing them to resume attempts immediately.

Is my system at risk according to Halo Surface Signal?

Systems using this software for authentication are considered high-priority targets. Halo Surface Signal notes that because TOTP is a core security control for identity services, the portals using it are inherently designed to be public-facing and internet-accessible. This accessibility means any application relying on a vulnerable version of this library is likely exposed to remote attackers attempting to brute-force credentials.

Do I need to update my openssl_encrypt implementation?

Your first step should be to inventory all applications in your environment to identify where this specific TOTP library is deployed. Once identified, evaluate the criticality of the services protected by these tokens. Coordinate with your development or platform teams to confirm if your current version is below 1.4.0 and prioritize applying the necessary updates or architectural changes provided by the maintainer to secure your authentication path.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.