CVE-2025-26524: RupeeWeb Trading Platform DoS Vulnerability

CVE-2025-26524 is a denial of service vulnerability in RupeeWeb trading platform caused by missing rate limiting on OTP requests. Attackers can exploit this to flood systems with OTP bombing attacks. This article covers technical details, affected versions, impact assessment, and mitigation strategies.

CVE-2025-26524 Overview

CVE-2025-26524 is a missing rate limiting vulnerability in the RupeeWeb trading platform. The flaw exists in certain API endpoints that handle One-Time Password (OTP) requests. An authenticated remote attacker can abuse these endpoints to trigger OTP bombing or flooding against a targeted user. The weakness is tracked under CWE-799: Improper Control of Interaction Frequency. The vulnerability was disclosed through the Indian Computer Emergency Response Team (CERT-In) in Vulnerability Note CIVN-2025-0020.

Critical Impact
Authenticated attackers can flood targeted users with OTP messages, degrading platform availability and enabling downstream abuse such as SMS cost inflation and social-engineering campaigns.

Affected Products

RupeeWeb trading platform (OTP-related API endpoints)
See CERT-In advisory CIVN-2025-0020 for specific affected versions

Discovery Timeline

2025-02-14 - CVE-2025-26524 published to the National Vulnerability Database (NVD)
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-26524

Vulnerability Analysis

The vulnerability stems from the absence of throttling controls on API endpoints that generate and dispatch OTPs. An authenticated user can repeatedly invoke these endpoints without being blocked or delayed. Each request causes the backend to generate and deliver a new OTP through SMS or email channels. Repeated invocation floods the recipient with messages, a technique commonly referred to as OTP bombing.

The impact is limited to availability of the messaging path and the user experience of the targeted account. Confidentiality and integrity are not directly affected. However, attackers frequently pair OTP flooding with social engineering to trick recipients into disclosing legitimate codes or approving fraudulent actions.

Root Cause

The root cause is missing enforcement of interaction frequency controls, as classified under CWE-799. The affected endpoints lack per-user, per-IP, and per-recipient counters that would normally cap the number of OTP requests within a defined time window. Without these controls, the API accepts unlimited OTP generation requests from an authenticated session.

Attack Vector

Exploitation requires network access to the API and valid authentication credentials on the platform. An attacker scripts repeated calls against a vulnerable OTP endpoint, supplying the target user's identifier. The server processes each call and dispatches a new OTP. Because no rate limit is enforced, the attacker sustains a high request volume until the target's inbox or SMS channel is saturated. Technical details of the exact endpoints are described in the CERT-In advisory referenced above.

Detection Methods for CVE-2025-26524

Indicators of Compromise

Sudden bursts of OTP generation events tied to a single authenticated session or source IP address.
Abnormally high SMS or email dispatch volume from the trading platform's messaging gateway.
Multiple OTP requests for the same recipient within short time intervals.
User complaints referencing unsolicited OTP messages arriving in rapid succession.

Detection Strategies

Instrument the OTP API endpoints with per-user and per-target request counters and log anomalies.
Correlate authentication logs with OTP dispatch logs to identify sessions generating outlier request volumes.
Alert when a single account triggers OTP requests targeting more than a threshold number of recipients per hour.

Monitoring Recommendations

Ingest API gateway and application logs into a centralized analytics platform for baseline and outlier analysis.
Track SMS and email provider usage metrics for cost spikes indicative of OTP flooding.
Monitor for authenticated sessions issuing repeated POST requests to OTP-related endpoints from a single source.

How to Mitigate CVE-2025-26524

Immediate Actions Required

Contact RupeeWeb and apply any fixes referenced in the CERT-In advisory CIVN-2025-0020.
Enforce server-side rate limiting on all OTP generation endpoints, keyed on user ID, target recipient, and source IP.
Introduce exponential backoff or CAPTCHA challenges after a small number of consecutive OTP requests.
Review authentication logs for accounts abusing OTP endpoints and revoke or reset compromised credentials.

Patch Information

Refer to the CERT-In Vulnerability Note CIVN-2025-0020 for the vendor's remediation guidance. At the time of publication, no vendor advisory URL is listed in NVD beyond the CERT-In reference. Contact RupeeWeb directly to confirm the fixed release.

Workarounds

Deploy an API gateway or web application firewall rule that limits OTP endpoint requests per session and per target.
Implement server-side cooldown windows (for example, 60 seconds) between successive OTP requests for the same recipient.
Cap daily OTP request volume per authenticated account and log or block excessive activity.
Require a second verification step, such as CAPTCHA, before generating additional OTPs after a threshold is reached.

bash

# Example NGINX rate-limit configuration for OTP endpoints
http {
    limit_req_zone $binary_remote_addr zone=otp_ip:10m rate=5r/m;
    limit_req_zone $http_authorization zone=otp_user:10m rate=5r/m;

    server {
        location /api/otp/request {
            limit_req zone=otp_ip burst=2 nodelay;
            limit_req zone=otp_user burst=2 nodelay;
            proxy_pass http://backend_otp_service;
        }
    }
}