CVE-2026-42391
Description
A flaw was found in Dovecot. An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in. This action causes the server to consume excessive memory and CPU resources, leading to the termination of login processes and other active connections. This can result in a degradation or complete denial of service for IMAP logins.
Mitigation
To mitigate this issue, limit the number of connections handled by a single `imap-login` process by adjusting the `process_limit` setting within the `service imap-login` block in your Dovecot configuration (e.g., `/etc/dovecot/dovecot.conf`). Increasing `process_limit` will cause Dovecot to spawn more `imap-login` processes, distributing connections more widely and reducing the impact of a single malicious connection.
For example, to set the process limit to 200:
# /etc/dovecot/dovecot.conf
service imap-login {
process_limit = 200
}
After modifying the configuration, restart the Dovecot service for the changes to take effect. This may impact performance due to increased process overhead.
bash
systemctl restart dovecot
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Resource Consumption (Other)
When allocating resources without limits, an attacker could prevent other systems, applications, or processes from accessing the same type of resource. It can be easy for an attacker to consume many resources by rapidly making many requests or causing larger resources to be used than is needed.
Frequently Asked Questions
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