CVE-2025-43857: net\ DoS — Fix

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.

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CVSS v3.1 Score

6.5

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-400 Uncontrolled Resource Consumption

CWE-405 CWE-405

CWE-770 CWE-770

CWE-789 CWE-789

Affected Products

Vendor	Product	Versions
ruby-lang	net\	< 0.2.5
ruby-lang	net\	0.3.0 — 0.3.9
ruby-lang	net\	0.4.0 — 0.4.20
ruby-lang	net\	0.5.0 — 0.5.7

References

Advisories & Patches

https://github.com/ruby/net-imap/pull/442 https://github.com/ruby/net-imap/pull/444/commits/0ae8576c1a90bcd9573f81bdad4b4b824642d105#diff-53721cb4d9c3fb86b95cc8476ca2df90968ad8c481645220c607034399151462 https://github.com/ruby/net-imap/pull/445 https://github.com/ruby/net-imap/pull/446 https://github.com/ruby/net-imap/pull/447 https://github.com/ruby/net-imap/security/advisories/GHSA-j3g3-5qv5-52mj

Frequently Asked Questions

What is CVE-2025-43857? +

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. It has a CVSS v3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2025-43857? +

CVE-2025-43857 has a CVSS v3.1 score of 6.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2025-43857? +

CVE-2025-43857 affects products from ruby-lang, specifically: net\. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-43857? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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