Summary
A vulnerability was identified in the variTRON password generation algorithm of the debug-interface. The PRNG is initialized with the current Unix Timestamp, thus the resulting password is predictable.
With the password root-access to the UART and ssh Interface can be gained.
The impact is limited, since the debug-interface has to be actively enabled by an authorized user and will be deactivated automatically after the next reboot of the device.
Details
Impact
Unauthorized root-access to the UART and ssh Interface.
Remediation
Update the affected products to version 9.0.2.5.
Mitigation
Disable the debug-interface to prevent unauthorized root-access to the UART and ssh Interface.
Vulnerabilities 1
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High 7.4
Jumo: Insufficient entropy in PRNG may lead to root access
A vulnerability was identified in the password generation algorithm when accessing the debug-interface. An unauthenticated local attacker with knowledge of the password generation timeframe might be able to brute force the password in a timely manner and thus…
Revision history
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#1.0.0
Release version.
References
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Jumo PSIRT
https://www.jumo.de
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CERT@VDE Security Advisories for Jumo
https://certvde.com/de/advisories/vendor/jumo/
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VDE-2025-086: Jumo: Predictable debug-interface password in variTRON series - HTML
https://certvde.com/en/advisories/VDE-2025-086