CVE-2025-29998: CAP Back Office API DoS Vulnerability

CVE-2025-29998 Overview

CVE-2025-29998 is a missing rate limiting vulnerability in the CAP back office application. The flaw resides in an API endpoint that handles One-Time Password (OTP) generation requests. An authenticated remote attacker can issue repeated OTP requests through the vulnerable endpoint without throttling controls. This behavior enables OTP bombing or flooding against targeted users of the system. The weakness is tracked under CWE-799: Improper Control of Interaction Frequency. CERT-In documented the issue in advisory CIVN-2025-0048.

Critical Impact
Authenticated attackers can flood targets with OTP messages, degrading availability of OTP delivery channels and enabling abuse of downstream SMS or email gateways.

Affected Products

CAP back office application (specific versions not disclosed in the public advisory)
API endpoint handling OTP generation requests
Downstream OTP delivery channels (SMS and email gateways)

Discovery Timeline

2025-03-13 - CVE-2025-29998 published to NVD
2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-29998

Vulnerability Analysis

The vulnerability stems from the absence of rate limiting on an OTP generation API endpoint within the CAP back office application. The endpoint accepts OTP requests from authenticated users but does not enforce a maximum number of requests per time window, per user, or per target identifier. As a result, an attacker holding valid credentials can submit a large volume of OTP requests in rapid succession. Each request triggers OTP generation and delivery to the target recipient, producing message floods on SMS or email channels. The EPSS score for this CVE is 0.629% with a percentile of 70.48, indicating moderate exploitation likelihood relative to other published CVEs.

Root Cause

The root cause is missing input frequency control on the OTP request handler. The API does not implement counters, token buckets, or backoff mechanisms tied to the requesting account or the OTP recipient. This matches CWE-799: Improper Control of Interaction Frequency, which describes systems that fail to restrict repeated actions over short intervals.

Attack Vector

The attack is network-based and requires authentication. An attacker with valid credentials scripts repeated calls to the OTP endpoint targeting a victim phone number or email address. The volume of generated OTPs floods the victim with notifications and consumes the application's SMS or email quota. Secondary effects include denial of legitimate OTP delivery, increased operational cost, and potential blocklisting by upstream telecom providers. No public proof-of-concept code is currently available for this issue. Refer to the CERT-In Advisory CIVN-2025-0048 for additional context.

Detection Methods for CVE-2025-29998

Indicators of Compromise

High volume of OTP generation API calls from a single authenticated session or source IP within short time windows
Repeated OTP requests targeting the same recipient phone number or email address
Unusual spikes in SMS or email gateway usage outside of normal business patterns
User complaints about receiving streams of unexpected OTP messages

Detection Strategies

Instrument the OTP endpoint with per-user and per-recipient request counters and alert on threshold breaches
Correlate authentication logs with OTP request logs to identify accounts issuing abnormal request volumes
Apply anomaly detection on SMS and email gateway billing records to surface sudden cost spikes
Review web application firewall (WAF) and API gateway logs for repetitive POST requests to the OTP endpoint

Monitoring Recommendations

Forward API gateway and application logs to a centralized analytics platform for continuous review
Set alerts when OTP requests exceed defined thresholds per account, recipient, or IP within a rolling window
Track failed and successful OTP deliveries separately to identify gateway saturation
Monitor authenticated session activity for behavioral deviations such as scripted request patterns

How to Mitigate CVE-2025-29998

Immediate Actions Required

Apply the vendor patch referenced in CERT-In Advisory CIVN-2025-0048 as soon as it is available
Enforce server-side rate limits on the OTP endpoint per user, per recipient, and per source IP
Add a minimum interval (for example, 30 to 60 seconds) between successive OTP requests for the same recipient
Audit recent OTP request logs for abusive patterns and revoke credentials of any accounts involved

Patch Information

Consult the CERT-In Advisory CIVN-2025-0048 for vendor-supplied remediation guidance. Apply the fixed version of the CAP back office application once released by the vendor and validate that rate limiting controls are active on the OTP endpoint post-deployment.

Workarounds

Deploy rate limiting at the API gateway or reverse proxy layer in front of the OTP endpoint
Introduce CAPTCHA or proof-of-work challenges for repeated OTP requests from the same session
Restrict OTP request access to specific authenticated roles and revoke unnecessary permissions
Configure SMS and email gateway quotas per account to cap downstream abuse impact

bash

# Example NGINX rate limit configuration for an OTP endpoint
limit_req_zone $binary_remote_addr zone=otp_ip:10m rate=5r/m;
limit_req_zone $http_authorization zone=otp_user:10m rate=3r/m;

location /api/otp/request {
    limit_req zone=otp_ip burst=2 nodelay;
    limit_req zone=otp_user burst=1 nodelay;
    limit_req_status 429;
    proxy_pass http://cap_backoffice_upstream;
}