User Enumeration Vulnerability in Dropbear SSH
Summary
ALPINE-CVE-2018-15599: The recv_msg_userauth_request function in svr-auth.c in Dropbear through 2018.76 is prone to a user enumeration vulnerability because username validity affects how fields in SSH_MSG_USERAUTH messages are handled, a simil... Affects dropbear versions < 2018.76-r2. Fixed in 2018.76-r2. How to fix ↓
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Background
Dropbear is a lightweight SSH server and client designed for environments with low resources. It is commonly used in embedded systems and provides secure remote access to devices. The package is known for its efficiency and ease of use, making it a popular choice for developers. However, it has been identified to have a user enumeration vulnerability that can potentially expose sensitive information about user accounts.
Vulnerability Detail
The vulnerability arises from the recv_msg_userauth_request function in svr-auth.c within Dropbear versions up to 2018.76. This flaw allows attackers to determine the validity of usernames based on how the SSH_MSG_USERAUTH messages are processed. This behavior is similar to a previously identified issue (CVE-2018-15473) in another codebase. The ramifications of this vulnerability include the potential for unauthorized access attempts and the risk of brute-force attacks, as attackers can ascertain valid usernames without needing to guess passwords.
How To Fix
Minimum fixed version
2018.76-r2
This is the first release that contains the fix.
sudo apk add --upgrade dropbearTip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, administrators can implement account lockout mechanisms after a certain number of failed login attempts to mitigate the risk of username enumeration.
Conclusion
The user enumeration vulnerability in Dropbear SSH poses a significant risk to systems using this package. It is crucial for users to update to the patched version to safeguard against potential attacks. Implementing additional security measures can further enhance protection against exploitation.
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FAQ
The CVSS score of this vulnerability is 5.3, indicating a moderate level of severity.
You can use Vulert's playground at Vulert Scanner to check if your application is affected by this vulnerability without needing to sign up.
The potential impacts include unauthorized access attempts and increased risk of brute-force attacks due to the ability to verify valid usernames.
Yes, implementing account lockout mechanisms after several failed login attempts can help mitigate the risk temporarily.
Dropbear is primarily used as a lightweight SSH server and client for secure remote access, especially in resource-constrained environments.
References
Related vulnerabilities
Recent vulnerabilities recorded for dropbear.
