# CVE-2026-36609: Mercusys AC12G V1 password recovery via static nonce and weak encoding

Source: https://junglewise.ai/threats/cve-2026-36609-mercusys-ac12g-v1-password-recovery-via-static-nonce-and-weak  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-03. Updated: 2026-06-03  
License: CC BY 4.0 with a link back

CVE-2026-36609 · Severity: info · CVSS 7.5 · Published 2026-06-03

The Mercusys AC12G router, a device used to provide home and small office internet connectivity, contains a security flaw in how it handles login credentials. Because the router uses predictable security codes and fails to change them between login attempts, an attacker who monitors network traffic can easily intercept and decode the administrator's password. This could allow an unauthorized person to take full control of the router, change network settings, or monitor user activity.

Technologies: [Mercusys AC12G](https://junglewise.ai/threats/technologies/ac12g). Vendors: [Mercusys](https://junglewise.ai/threats/vendors/mercusys).

## Quick answers

**Is CVE-2026-36609 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-36609 being exploited in the wild.

**How severe is CVE-2026-36609?** Informational severity, with a CVSS score of 7.5, published 3 June 2026.

**Which products and versions are affected?** Mercusys AC12G AC12G(EU)_V1_200909, AC12G(EU)_V1_210128.

**Is there a fix for CVE-2026-36609?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-36609 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-36609?** Check whether you run Mercusys AC12G at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The Mercusys AC12G (EU) V1 router's authentication mechanism (TDDP protocol) utilizes a static 32-character nonce that is generated only once per boot per source IP. The password encoding process, handled by the 'securityEncode' function in /lib/Quary.js, employs a simple XOR-based scheme with a hardcoded salt ('RDpbLfCPsJZ7fiv'). Because the nonce is static and the encoding is deterministic and reversible, a network-based attacker can capture an authentication token and reverse it to recover the plaintext password. Additionally, the lack of token rotation or expiration allows for indefinite session replay and offline dictionary attacks. The product is reportedly end-of-life, and no official patch is expected.

## Affected products

- Mercusys AC12G (EU) V1 AC12G(EU)_V1_200909, AC12G(EU)_V1_210128

## Timeline

- 2026-06-03: advisory: NVD and researcher advisory published

## References

- [https://github.com/Tymbark7372/MERCUSYS-AC12G/blob/master/advisories/CVE-2026-36609.md](https://github.com/Tymbark7372/MERCUSYS-AC12G/blob/master/advisories/CVE-2026-36609.md)

## Related threats

- [Mercusys AC12G hardcoded WiFi credentials in firmware](https://junglewise.ai/threats/cve-2026-36616-mercusys-ac12g-hardcoded-wifi-credentials-in-firmware)
- [Mercusys AC12G information disclosure in /agileconfigreset endpoint](https://junglewise.ai/threats/cve-2026-36615-mercusys-ac12g-information-disclosure-in-agileconfigreset)
- [Mercusys AC12G uninitialized buffer disclosure in UPnP](https://junglewise.ai/threats/cve-2026-36611-mercusys-ac12g-uninitialized-buffer-disclosure-in-upnp)
- [Mercusys AC12G UPnP port forwarding to local admin interface](https://junglewise.ai/threats/cve-2026-36608-mercusys-ac12g-upnp-port-forwarding-to-local-admin-interface)
- [Mercusys AC12G hardcoded DES key in configuration backup](https://junglewise.ai/threats/cve-2026-36606-mercusys-ac12g-hardcoded-des-key-in-configuration-backup)