Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. From versions 0.4.0 to before 0.4.24, 0.5.0 to before 0.5.14, and 0.6.0 to before 0.6.4, when authenticating a connection with SCRAM-SHA1 or SCRAM-SHA256, a hostile server can perform a computational denial-of-service attack on the client process by sending a big iteration count value. This issue has been patched in versions 0.4.24, 0.5.14, and 0.6.4.

The remote openSUSE 16 host has packages installed that are affected by a vulnerability as referenced in the openSUSE- SU-2026:21225-1 advisory.

    This update for rmt-server fixes the following issue

    Update to 3.0.0:

    - CVE-2026-42256: net-imap: hostile server can perform a DoS on client authenticating a connection with     SCRAM-SHA1 or       SCRAM-SHA2 (bsc#1265369).

    Changes for rmt-server:

    - Version 3.0.0
     * Security fix: Remove unused ActionMailer/ActionMailbox components to      eliminate CVE-2026-42256 (bsc#1265369)
     * Split Rails meta-gem into individual components for better security control
    - Version 2.26
     * Add support for processing, storing, and syncing system profiles (jsc#TEL-265)
    - Version 2.25
     * fix rmt-cli list and purge commands for large data (bsc#1253146 and bsc#1253147)
     * Fix mirroring of SLE16 NVIDIA-GPU-Compute-Toolkit-CUDA repo (bsc#1256826)
     * Support for new redirect_repo_hosts config, to exclude some repo hosts      from mirroring, and send clients directly there (jsc#SCC-452)
     * rmt-server-pubcloud
     * Clearer error message (bsc#1256883)
     * Handle zypper response when data exporter raises an error (bsc#1257133)
     * Add Valkey + Sidekiq for async processing
     * Enable mirroring xz compressed repositories (bsc#1246976)
     * Rack 2.2.20 security update (bsc#1253953, bsc#1251937)
     * Drop some de-published products from RMT
     * Include Live-Patching for SLES 15.X (jsc#PCT-630)
     * Handle only one data exporter (bsc#1248869)
     * Do not decode instance data from db to access registry (bsc#1248510)
     * Handle instance verification exceptions

Tenable has extracted the preceding description block directly from the SUSE security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2023-2026-1807 advisory.

    zlib is a Ruby interface for the zlib compression/decompression library. Versions 3.0.0 and below, 3.1.0,     3.1.1, 3.2.0 and 3.2.1 contain a buffer overflow vulnerability in the Zlib::GzipReader. The     zstream_buffer_ungets function prepends caller-provided bytes ahead of previously produced output but     fails to guarantee the backing Ruby string has enough capacity before the memmove shifts the existing     data. This can lead to memory corruption when the buffer length exceeds capacity. This issue has been     fixed in versions 3.0.1, 3.1.2 and 3.2.3. (CVE-2026-27820)

    Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to     versions 0.4.24, 0.5.14, and 0.6.4, Net::IMAP::ResponseReader has quadratic time complexity when reading     large responses containing many string literals. A hostile server can send responses which are crafted to     exhaust the client's CPU for a denial of service attack. This issue has been patched in versions 0.4.24,     0.5.14, and 0.6.4. (CVE-2026-42245)

    Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to     versions 0.3.10, 0.4.24, 0.5.14, and 0.6.4, a man-in-the-middle attacker can cause Net::IMAP#starttls to     return successfully, without starting TLS. This issue has been patched in versions 0.3.10, 0.4.24,     0.5.14, and 0.6.4. (CVE-2026-42246)

    Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. From versions     0.4.0 to before 0.4.24, 0.5.0 to before 0.5.14, and 0.6.0 to before 0.6.4, when authenticating a     connection with SCRAM-SHA1 or SCRAM-SHA256, a hostile server can perform a computational denial-of-service     attack on the client process by sending a big iteration count value. This issue has been patched in     versions 0.4.24, 0.5.14, and 0.6.4. (CVE-2026-42256)

    Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to     versions 0.4.24, 0.5.14, and 0.6.4, several Net::IMAP commands accept a raw string argument that is sent     to the server without validation or escaping. If this string is derived from user-controlled input, it may     contain contain CRLF sequences, which an attacker can use to inject arbitrary IMAP commands. This issue     has been patched in versions 0.4.24, 0.5.14, and 0.6.4. (CVE-2026-42257)

    Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to     versions 0.4.24, 0.5.14, and 0.6.4, symbol arguments to commands are vulnerable to a CRLF Injection / IMAP     Command injection via Symbol arguments passed to IMAP commands. This issue has been patched in versions     0.4.24, 0.5.14, and 0.6.4. (CVE-2026-42258)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. From versions     0.4.0 to before 0.4.24, 0.5.0 to before 0.5.14, and 0.6.0 to before 0.6.4, when authenticating a     connection with SCRAM-SHA1 or SCRAM-SHA256, a hostile server can perform a computational denial-of-service     attack on the client process by sending a big iteration count value. This issue has been patched in     versions 0.4.24, 0.5.14, and 0.6.4. (CVE-2026-42256)

Note that Nessus relies on the presence of the package as reported by the vendor.

The version of the net-imap Ruby library installed on the remote host is prior to 0.4.x prior to 0.4.24, 0.5.x prior to 0.5.14, or 0.6.x prior to 0.6.4. It is, therefore, affected by a computational denial-of-service vulnerability.

A denial of service vulnerability exists when authenticating a connection via SCRAM-SHA1 or SCRAM-SHA256. A malicious server can exploit this by sending an excessively high iteration count value, resulting in significant CPU consumption on the client process. This computational overhead can be used to perform a denial of service attack against the connecting client.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. From versions
    0.4.0 to before 0.4.24, 0.5.0 to before 0.5.14, and 0.6.0 to before 0.6.4, when authenticating a
    connection with SCRAM-SHA1 or SCRAM-SHA256, a hostile server can perform a computational denial-of-service
    attack on the client process by sending a big iteration count value. This issue has been patched in
    versions 0.4.24, 0.5.14, and 0.6.4. (CVE-2026-42256)

ID	Name	Product	Family	Severity
325255	openSUSE 16: ansible-rmt-server / rmt-server / rmt-server-config / etc (openSUSE-SU-2026:21225-1)	Nessus	SuSE Local Security Checks	medium
319837	Amazon Linux 2023 : ruby3.4, ruby3.4-bundled-gems, ruby3.4-default-gems (ALAS2023-2026-1807)	Nessus	Amazon Linux Local Security Checks	high
315697	Linux Distros Unpatched Vulnerability : CVE-2026-42256	Nessus	Misc.	medium
313277	Ruby net-imap 0.4.x < 0.4.24 / 0.5.x < 0.5.14 / 0.6.x < 0.6.4 vulnerability	Nessus	Misc.	medium
441081	SCA: security update for net-imap (GHSA-87pf-fpwv-p7m7)	Tenable Cloud Security	SCA Checks	medium
441081	SCA: security update for net-imap (GHSA-87pf-fpwv-p7m7)	Tenable Self-Hosted Container Security	SCA Checks	medium

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CVE-2026-42256

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Tenable Plugins

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high

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medium