CVE-2026-31848: Reversible ecos_pw Cookie Allows Authentication Bypass in Nexxt Nebula 300+

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-23 · updated 2026-08-10
Weakness: CWE-312

Description

Nexxt Solutions Nebula 300+ firmware through version 12.01.01.37 uses the ecos_pw cookie for authentication, which contains Base64-encoded credential data combined with a static suffix. Because the encoding is reversible and lacks integrity protection, an attacker can reconstruct or forge a valid cookie value without proper authentication.

Affected products

Nexxtsolutions Nebula300Plus Firmware: through 12.01.01.37

References

https://nexxt-connectivity-frontend.s3.amazonaws.com/media/docs/Nebula300+_v12.01.01.37.zip
https://www.nexxtsolutions.com/connectivity/internal-products/ARN02304U6/

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