CVE-2025-29998: CAP Back Office OTP Flooding Vulnerability

CVE-2025-29998 Overview

CVE-2025-29998 affects the CAP back office application and stems from missing rate limiting on One-Time Password (OTP) requests in an API endpoint. An authenticated remote attacker can submit repeated OTP requests through the vulnerable endpoint, triggering OTP bombing or flooding against targeted users. The flaw maps to CWE-799: Improper Control of Interaction Frequency and was disclosed through CERT-In Security Advisory CIVN-2025-0048. The vulnerability impacts availability of the OTP delivery channel and the messaging or email infrastructure used to dispatch codes.

Critical Impact

Authenticated attackers can flood the OTP delivery system, exhaust messaging resources, and disrupt legitimate authentication workflows.

Affected Products

• CAP back office application (as listed in CERT-In advisory CIVN-2025-0048)
• Specific version information was not published in the available references
• Refer to the CERT-In advisory for vendor-supplied product details

Discovery Timeline

• 2025-03-13 - CVE-2025-29998 published to the National Vulnerability Database
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-29998

Vulnerability Analysis

The vulnerability resides in an OTP request API endpoint of the CAP back office application. The endpoint does not enforce a frequency or rate limit on inbound requests from authenticated callers. An attacker who holds valid credentials can script repeated calls to the endpoint, each of which causes the backend to generate and dispatch an OTP to a target recipient.

This behavior produces two compounding effects. First, the targeted user receives a flood of OTP messages via SMS, email, or push notification, creating a denial-of-service condition against the recipient and the delivery channel. Second, the backend SMS or email gateway consumes quota, budget, and processing capacity that legitimate users depend on. CWE-799 categorizes this class of weakness as Improper Control of Interaction Frequency.

Root Cause

The root cause is the absence of server-side throttling controls on the OTP generation endpoint. Effective OTP flows require per-account, per-IP, and per-recipient rate limits, cooldown windows between successive requests, and CAPTCHA or proof-of-work challenges. None of these controls are enforced on the affected endpoint, allowing automated abuse.

Attack Vector

The attack requires network access to the API and valid authentication to the CAP back office. The attacker authenticates, identifies the OTP request endpoint, and issues repeated requests targeting a victim identifier such as a phone number or email address. No user interaction is required on the victim side. The exploitation flow does not require code execution or memory corruption primitives - it is a logic and policy abuse of a normal API.

No verified public proof-of-concept code is referenced in the advisory.

Detection Methods for CVE-2025-29998

Indicators of Compromise

• High-frequency requests to the OTP generation endpoint originating from a single authenticated session or API token
• Spikes in outbound SMS or email volume from the OTP delivery service without a corresponding rise in successful logins
• Multiple OTP requests targeting the same recipient identifier within short time windows
• User complaints reporting unsolicited OTP messages received in rapid succession

Detection Strategies

• Instrument the OTP endpoint with per-account, per-IP, and per-target counters and alert when thresholds are exceeded
• Correlate authentication logs with OTP dispatch logs to identify sessions generating disproportionate request volumes
• Baseline normal OTP request rates per user and flag statistical outliers using anomaly identification

Monitoring Recommendations

• Forward API access logs, authentication events, and SMS/email gateway telemetry to a centralized analytics platform for correlation
• Track OTP delivery cost and quota consumption as a security signal, not only as a billing metric
• Monitor for authenticated accounts that suddenly shift behavior from interactive use to scripted high-volume API calls

How to Mitigate CVE-2025-29998

Immediate Actions Required

• Apply the vendor patch or update referenced in CERT-In advisory CIVN-2025-0048 once available for your deployment
• Deploy a Web Application Firewall (WAF) or API gateway rule that limits requests to the OTP endpoint per source identity and per target recipient
• Audit recent OTP dispatch logs for anomalous volumes and notify any users who received unsolicited OTP floods

Patch Information

Refer to the CERT-In Security Advisory CIVN-2025-0048 for vendor-supplied remediation guidance and fixed version details. No additional vendor advisory URLs were published in the enriched CVE record at the time of writing.

Workarounds

• Enforce rate limits at the reverse proxy or API gateway layer until the upstream fix is deployed
• Add CAPTCHA or progressive delays to OTP request flows to break automated abuse loops
• Implement a server-side cooldown that rejects repeat OTP requests for the same recipient within a defined interval
• Cap daily OTP volume per account and per recipient and alert on threshold breaches

# Example NGINX rate limit for an OTP endpoint
# Limit each client IP to 1 request every 30 seconds with a small burst
http {
    limit_req_zone $binary_remote_addr zone=otp_zone:10m rate=2r/m;

    server {
        location /api/otp/request {
            limit_req zone=otp_zone burst=2 nodelay;
            limit_req_status 429;
            proxy_pass http://cap_backoffice_upstream;
        }
    }
}