CVE-2025-43857: net-imap rubygem vulnerable to possible DoS by memory exhaustion

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-04-28 · updated 2026-06-17
Weakness: CWE-400

Description

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to versions 0.5.7, 0.4.20, 0.3.9, and 0.2.5, there is a possibility for denial of service by memory exhaustion when net-imap reads server responses. At any time while the client is connected, a malicious server can send can send a "literal" byte count, which is automatically read by the client's receiver thread. The response reader immediately allocates memory for the number of bytes indicated by the server response. This should not be an issue when securely connecting to trusted IMAP servers that are well-behaved. It can affect insecure connections and buggy, untrusted, or compromised servers (for example, connecting to a user supplied hostname). This issue has been patched in versions 0.5.7, 0.4.20, 0.3.9, and 0.2.5.

Affected products

ruby-lang Net::Imap: before 0.2.5; from 0.3.0 before 0.3.9; from 0.4.0 before 0.4.20; from 0.5.0 before 0.5.7 — fixed in 0.2.5, 0.3.9, 0.4.20, 0.5.7

How to fix

Upgrade to a fixed version: ruby-lang Net::Imap 0.2.5, 0.3.9, 0.4.20, 0.5.7. Check the vendor advisory for mitigations.

References

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