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Ubuntu 16.04 LTS / 18.04 LTS : Ruby vulnerabilities (USN-8431-1)

high Nessus Plugin ID 321185

Synopsis

The remote Ubuntu host is missing one or more security updates.

Description

The remote Ubuntu 16.04 LTS / 18.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8431-1 advisory.

 It was discovered that Ruby's Net::IMAP library did not properly verify that Transport Layer Security (TLS) encryption was started after issuing a STARTTLS command. A remote attacker could possibly use this issue to perform a machine-in-the-middle attack and silently bypass TLS encryption. (CVE-2026-42246)

 It was also discovered that Ruby's Net::IMAP library did not validate string arguments passed to certain commands. A remote attacker could possibly use this issue to inject arbitrary IMAP commands.
 (CVE-2026-42257)

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

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

Solution

Update the affected packages.

See Also

https://ubuntu.com/security/notices/USN-8431-1

Plugin Details

Severity: High

ID: 321185

File Name: ubuntu_USN-8431-1.nasl

Version: 1.1

Type: Local

Agent: unix

Published: 6/16/2026

Updated: 6/16/2026

Supported Sensors: Continuous Assessment, Nessus Agent, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 6.7

CVSS v2

Risk Factor: Critical

Base Score: 10

Temporal Score: 7.4

Vector: CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:C

CVSS Score Source: CVE-2026-42257

CVSS v3

Risk Factor: Critical

Base Score: 9.8

Temporal Score: 8.5

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

CVSS v4

Risk Factor: High

Base Score: 7.6

Threat Score: 4.9

Threat Vector: CVSS:4.0/E:U

Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

CVSS Score Source: CVE-2026-42246

Vulnerability Information

CPE: p-cpe:/a:canonical:ubuntu_linux:ruby2.3-dev, p-cpe:/a:canonical:ubuntu_linux:ruby2.5, cpe:/o:canonical:ubuntu_linux:16.04:-:lts, cpe:/o:canonical:ubuntu_linux:18.04:-:lts, p-cpe:/a:canonical:ubuntu_linux:ruby2.3-tcltk, p-cpe:/a:canonical:ubuntu_linux:libruby2.5, p-cpe:/a:canonical:ubuntu_linux:ruby2.5-dev, p-cpe:/a:canonical:ubuntu_linux:ruby2.3, p-cpe:/a:canonical:ubuntu_linux:libruby2.3

Required KB Items: Host/cpu, Host/Ubuntu, Host/Ubuntu/release, Host/Debian/dpkg-l

Exploit Ease: No known exploits are available

Patch Publication Date: 6/15/2026

Vulnerability Publication Date: 5/4/2026

Reference Information

CVE: CVE-2026-42246, CVE-2026-42257

USN: 8431-1