Security researchers at SEC Consult (Eviden) uncovered a critical flaw in certain KioSoft prepaid NFC cards that power self-service payments in laundromats, vending machines, arcades, and car washes. Tracked as CVE-2025-8699, the issue allowed attackers to raise a card’s stored balance without payment. The coordinated disclosure spanned more than a year, with fixes reportedly shipped in summer 2025.
What happened: Stored-value manipulation in KioSoft’s NFC ecosystem
KioSoft reports more than 41,000 kiosks and 1.6 million payment terminals across 35 countries. According to SEC Consult, only a subset of deployments using specific prepaid cards were affected. The root of the problem was architectural: the balance was stored on the card itself rather than enforced by a protected backend service, making it susceptible to tampering.
Root cause: Legacy MIFARE Classic weaknesses
The impacted cards relied on MIFARE Classic, a legacy RFID technology whose proprietary CRYPTO1 cipher and authentication scheme were broken in widely cited research from 2007–2008. Those studies demonstrated practical key recovery and sector read/write attacks, enabling cloning and value manipulation. By analyzing KioSoft’s on-card data structure, researchers were able to read and modify balances directly.
Attack prerequisites and real-world impact
The attack required commodity RFID hardware—such as a Proxmark device—and familiarity with MIFARE Classic weaknesses. SEC Consult reports that balances could be increased up to $655 per operation, and the process could be repeated, effectively generating funds without a legitimate transaction. For operators, this translates into immediate revenue loss and chargeback-like disputes, alongside erosion of customer trust.
Disclosure timeline and vendor response
SEC Consult first reached out to KioSoft in October 2023. A vendor response followed after CERT facilitation, and KioSoft subsequently requested multiple extensions to the disclosure timeline. The company later stated that an updated firmware was released in summer 2025 and that it is planning new hardware with strengthened security controls.
KioSoft did not disclose version numbers for vulnerable or remediated builds, indicating customers would be notified directly. The vendor also emphasized that most KioSoft solutions do not rely on MIFARE Classic. SEC Consult noted it no longer had access to the original terminals and therefore could not independently validate the effectiveness of the patches.
Risk analysis: Offline stored value vs. server-side validation
Offline stored-value models are convenient and resilient to connectivity issues but materially increase fraud risk: a compromised card becomes a bearer instrument that can be modified outside normal controls. The industry trend favors stronger designs: MIFARE DESFire EV2/EV3 with AES and Security Level 3 (SL3), per-card key diversification, and server-side accounting with signed transaction logs and anomaly monitoring.
Recommendations for terminal operators and integrators
- Phase out MIFARE Classic in favor of DESFire EV2/EV3 with AES and mutual authentication (SL3) enabled.
- Shift from on-card balances to a centralized billing platform, using the card as an access token, not as the value store.
- Bind cards to customer accounts, enforce top-up limits, and deploy behavioral analytics to flag anomalies (e.g., rapid successive maximum loads).
- Implement key diversification per card/sector, anti-tearing, secure counters, and cryptographic signing of value blocks.
- Maintain current firmware, inventory all terminals, and schedule periodic third‑party penetration testing including RFID/NFC threat modeling.
Incidents like CVE-2025-8699 underscore that long-known weaknesses in legacy RFID technologies remain exploitable for years when left in production. Organizations should formalize coordinated vulnerability disclosure with vendors, adhere to industry timelines for remediation, and prioritize rapid deployment of fixes. For any environment using offline payments, resilience hinges on modern cryptography, server-side validation, and continuous anomaly detection. If you operate self-service payment infrastructure, initiate a portfolio-wide review of card technologies and firmware today and plan a staged migration to hardened, AES-based solutions.
