Resource Exhaustion Vulnerability in Dovecot: Large Header Handling
Summary
CVE-2024-23185: Very large headers can cause resource exhaustion when parsing message. Affects dovecot versions < 2.3.21.1-r0. Fixed in 2.3.21.1-r0. How to fix ↓
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Background
Dovecot is an open-source IMAP and POP3 server for Unix-like operating systems, designed to provide secure and efficient email retrieval and storage. It is widely used for its performance and flexibility, allowing users to manage their email accounts with ease. However, Dovecot is susceptible to a vulnerability that arises from the handling of very large headers, which can lead to resource exhaustion.
Vulnerability Detail
The vulnerability, identified as CVE-2024-23185, occurs when Dovecot's message-parser processes incoming messages with excessively large headers. The message-header-parser builds a 'full_value' buffer from smaller chunks of the message without imposing a size limit. This can result in significant memory usage, potentially leading to denial of service (DoS) for the user. Although incoming mails typically have size limits set by the Mail Transfer Agent (MTA), users can still append larger mails, which may cause memory issues for the backend and allow them to DoS themselves.
How To Fix
Minimum fixed version
2.3.21.1-r0
This is the first release that contains the fix.
sudo apk add --upgrade dovecotTip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, implement restrictions on header sizes at the MTA component preceding Dovecot. This can help mitigate the risk of resource exhaustion by limiting the size of headers that Dovecot has to process.
Conclusion
CVE-2024-23185 represents a significant vulnerability in Dovecot related to the handling of large headers, which can lead to resource exhaustion. Users are advised to update their installations to the latest versions to mitigate this risk. Implementing MTA-level restrictions on header sizes can also serve as a temporary workaround.
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FAQ
CVE-2024-23185 is a vulnerability in Dovecot that allows for resource exhaustion due to the handling of very large headers in incoming messages.
If you are using a version of Dovecot prior to the fixed versions mentioned, your installation may be vulnerable. You can check your version by running 'dovecot --version' in the terminal.
The primary impact is resource exhaustion, which can lead to denial of service for users, especially if they append large mails to their accounts.
Yes, you can use Vulert to monitor and alert for open-source vulnerabilities in your software. It requires only a manifest file like package-lock.json to operate.
Vulert is a tool that allows you to monitor open-source vulnerabilities in real-time without needing to access the code or installation. You can check your application for vulnerabilities using the Vulert playground at Vulert Scanner.
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