USN-8431-1

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)

References

Affected packages

Ubuntu:Pro:16.04:LTS / ruby2.3

Package

Name: ruby2.3
Purl: pkg:deb/ubuntu/ruby2.3?arch=source&distro=esm-infra-legacy%2Fxenial

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0Unknown introduced version / All previous versions are affected

Fixed

2.3.1-2~ubuntu16.04.16+esm14

Affected versions

2.*

2.3.0-1

2.3.0-2

2.3.0-4ubuntu2

2.3.0-4ubuntu3

2.3.0-5ubuntu1

2.3.1-2~16.04

2.3.1-2~16.04.2

2.3.1-2~16.04.4

2.3.1-2~16.04.5

2.3.1-2~16.04.6

2.3.1-2~16.04.7

2.3.1-2~16.04.9

2.3.1-2~16.04.10

2.3.1-2~16.04.11

2.3.1-2~16.04.12

2.3.1-2~ubuntu16.04.13

2.3.1-2~ubuntu16.04.14

2.3.1-2~ubuntu16.04.15

2.3.1-2~ubuntu16.04.16

2.3.1-2~ubuntu16.04.16+esm1

2.3.1-2~ubuntu16.04.16+esm2

2.3.1-2~ubuntu16.04.16+esm3

2.3.1-2~ubuntu16.04.16+esm4

2.3.1-2~ubuntu16.04.16+esm5

2.3.1-2~ubuntu16.04.16+esm6

2.3.1-2~ubuntu16.04.16+esm7

2.3.1-2~ubuntu16.04.16+esm8

2.3.1-2~ubuntu16.04.16+esm9

2.3.1-2~ubuntu16.04.16+esm10

2.3.1-2~ubuntu16.04.16+esm11

2.3.1-2~ubuntu16.04.16+esm12

Ecosystem specific

{
    "binaries": [
        {
            "binary_version": "2.3.1-2~ubuntu16.04.16+esm14",
            "binary_name": "libruby2.3"
        },
        {
            "binary_version": "2.3.1-2~ubuntu16.04.16+esm14",
            "binary_name": "ruby2.3"
        },
        {
            "binary_version": "2.3.1-2~ubuntu16.04.16+esm14",
            "binary_name": "ruby2.3-tcltk"
        }
    ],
    "availability": "Available with Ubuntu Pro with Legacy support add-on: https://ubuntu.com/pro"
}

Database specific

source

"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/usn/USN-8431-1.json"

cves_map

{
    "cves": [
        {
            "severity": [
                {
                    "score": "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",
                    "type": "CVSS_V4"
                },
                {
                    "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N",
                    "type": "CVSS_V3"
                },
                {
                    "score": "medium",
                    "type": "Ubuntu"
                }
            ],
            "id": "CVE-2026-42246"
        },
        {
            "severity": [
                {
                    "score": "CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N",
                    "type": "CVSS_V4"
                },
                {
                    "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
                    "type": "CVSS_V3"
                },
                {
                    "score": "medium",
                    "type": "Ubuntu"
                }
            ],
            "id": "CVE-2026-42257"
        }
    ],
    "ecosystem": "Ubuntu:Pro:16.04:LTS"
}

Ubuntu:Pro:18.04:LTS / ruby2.5

Package

Name: ruby2.5
Purl: pkg:deb/ubuntu/ruby2.5?arch=source&distro=esm-infra%2Fbionic

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0Unknown introduced version / All previous versions are affected

Fixed

2.5.1-1ubuntu1.16+esm8

Affected versions

2.*

2.5.0~preview1-1ubuntu2

2.5.0-4ubuntu1

2.5.0-4ubuntu4

2.5.0-5ubuntu1

2.5.0-6ubuntu1

2.5.1-1ubuntu1

2.5.1-1ubuntu1.1

2.5.1-1ubuntu1.2

2.5.1-1ubuntu1.4

2.5.1-1ubuntu1.5

2.5.1-1ubuntu1.6

2.5.1-1ubuntu1.7

2.5.1-1ubuntu1.8

2.5.1-1ubuntu1.9

2.5.1-1ubuntu1.10

2.5.1-1ubuntu1.11

2.5.1-1ubuntu1.12

2.5.1-1ubuntu1.13

2.5.1-1ubuntu1.14

2.5.1-1ubuntu1.15

2.5.1-1ubuntu1.16

2.5.1-1ubuntu1.16+esm1

2.5.1-1ubuntu1.16+esm3

2.5.1-1ubuntu1.16+esm4

2.5.1-1ubuntu1.16+esm5

2.5.1-1ubuntu1.16+esm6

2.5.1-1ubuntu1.16+esm7

Ecosystem specific

{
    "binaries": [
        {
            "binary_version": "2.5.1-1ubuntu1.16+esm8",
            "binary_name": "libruby2.5"
        },
        {
            "binary_version": "2.5.1-1ubuntu1.16+esm8",
            "binary_name": "ruby2.5"
        }
    ],
    "availability": "Available with Ubuntu Pro (Infra-only): https://ubuntu.com/pro"
}

Database specific

source

"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/usn/USN-8431-1.json"

cves_map

{
    "cves": [
        {
            "severity": [
                {
                    "score": "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",
                    "type": "CVSS_V4"
                },
                {
                    "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N",
                    "type": "CVSS_V3"
                },
                {
                    "score": "medium",
                    "type": "Ubuntu"
                }
            ],
            "id": "CVE-2026-42246"
        },
        {
            "severity": [
                {
                    "score": "CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N",
                    "type": "CVSS_V4"
                },
                {
                    "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
                    "type": "CVSS_V3"
                },
                {
                    "score": "medium",
                    "type": "Ubuntu"
                }
            ],
            "id": "CVE-2026-42257"
        }
    ],
    "ecosystem": "Ubuntu:Pro:18.04:LTS"
}