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Ubuntu 16.04 LTS : Ruby vulnerabilities (USN-8556-1)

medium Nessus Plugin ID 327617

Synopsis

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

Description

The remote Ubuntu 16.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8556-1 advisory.

 It was discovered that the Net::IMAP client in Ruby did not properly sanitize Symbol arguments passed to IMAP commands. A remote attacker controlling a malicious IMAP server, or able to influence command arguments, could use this to inject arbitrary IMAP commands via CRLF sequences. (CVE-2026-42258)

 It was discovered that the Zlib::GzipReader in Ruby did not correctly ensure sufficient buffer capacity in the zstream_buffer_ungets function. An attacker could use this to craft a gzip stream that, when processed, could cause a buffer overflow, resulting in memory corruption and possibly arbitrary code execution. (CVE-2026-27820)

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-8556-1

Plugin Details

Severity: Medium

ID: 327617

File Name: ubuntu_USN-8556-1.nasl

Version: 1.1

Type: Local

Agent: unix

Published: 7/17/2026

Updated: 7/17/2026

Supported Sensors: Continuous Assessment, Nessus Agent, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.9

Percentile: 57.97

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-2026-27820

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: Medium

Base Score: 6.3

Threat Score: 1.7

Threat Vector: CVSS:4.0/E:U

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

Vulnerability Information

CPE: p-cpe:/a:canonical:ubuntu_linux:ruby2.3-dev, cpe:/o:canonical:ubuntu_linux:16.04:-:lts, p-cpe:/a:canonical:ubuntu_linux:ruby2.3-tcltk, 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: 7/16/2026

Vulnerability Publication Date: 4/16/2026

Reference Information

CVE: CVE-2026-27820, CVE-2026-42258

USN: 8556-1