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Amazon Linux 2023 : ruby4.0, ruby4.0-bundled-gems, ruby4.0-default-gems (ALAS2023-2026-2144)

medium Nessus Plugin ID 345799

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Synopsis

The remote Amazon Linux 2023 host is missing a security update.

Description

It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2023-2026-2144 advisory.

 An issue was discovered in the resolv gem before 0.7.2 for Ruby. Resolv::DNS::Resource.get_class, Resolv::DNS::Resource::Generic.create, and Resolv::DNS::SvcParam::Generic.create generate a new class for each unknown DNS resource record (type, class) pair, or each unknown SvcParamKey, encountered while decoding a response. Each generated class was permanently registered both as a constant on Resource (or SvcParam::Generic) and as an entry in a class-lookup hash (ClassHash), and thus the class remained reachable through that constant after the response was discarded. Type and class are each 16-bit values, and thus an attacker controlling DNS responses (a spoofed response, or a malicious or hijacked upstream DNS server) has roughly 2^32 distinct (type, class) pairs to choose from. A single response of a few hundred kilobytes carrying tens of thousands of distinct unknown types permanently grows process memory by tens of megabytes; repeated responses accumulate without bound and are never reclaimed by garbage collection, because the constant keeps each class alive. Any code path that calls Resolv::DNS::Message.decode on attacker-influenced DNS responses is affected. resolv is a default gem, and thus this is reachable from a plain Ruby installation without any additional dependency. (CVE-2026-80212)

 An issue was discovered in the resolv gem before 0.7.2 for Ruby. Resolv::DNS::MessageEncoder wrote a DNS label's length into a single octet without checking its range. A label longer than 255 octets had its length stored modulo 256 but the label data was written unchanged, and thus the bytes on the wire described a different name than the one the application asked to encode. RFC 1035 section 2.3.4 limits a label to 63 octets, and the two high bits of the length octet are reserved for compression pointers.
 put_string packed the length with put_pack(C, d.length) and put_label used it for labels, and thus any value from 0 to 255 could end up as a label length octet, including the reserved 0x40-0xBF range and the 0xC0-0xFF pointer range. Resolv::DNS::Name.create did not check per-label or total name length either, and thus an attacker-controlled hostname reached the encoder unchanged. An application that resolves an attacker-controlled hostname sends a query whose wire bytes name a domain the attacker chose. A hostname suffix that the application validates against an allowlist becomes padding that never appears on the wire, and thus allowlist and egress checks can be bypassed. The recursive resolver caches the response under the attacker's name, and DNS logs record that name rather than the one the application asked for. A label length whose low octet lands in the 0xC0-0xFF range produces a length octet that conforming parsers read as the start of a compression pointer, with the following attacker-controlled byte as the offset.
 (CVE-2026-80213)

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.

Solution

Run 'dnf update ruby4.0 --releasever 2023.12.20260914' or or 'dnf update --advisory ALAS2023-2026-2144 --releasever 2023.12.20260914' to update your system.

See Also

https://alas.aws.amazon.com//AL2023/ALAS2023-2026-2144.html

https://alas.aws.amazon.com/faqs.html

https://explore.alas.aws.amazon.com/CVE-2026-80212.html

https://explore.alas.aws.amazon.com/CVE-2026-80213.html

Plugin Details

Severity: Medium

ID: 345799

File Name: al2023_ALAS2023-2026-2144.nasl

Version: 1.1

Type: Local

Agent: unix

Published: 9/14/2026

Updated: 9/14/2026

Supported Sensors: Frictionless Assessment AWS, Frictionless Assessment Agent, Nessus Agent, Agentless Assessment, Continuous Assessment, Tenable Cloud Security, Tenable Self-Hosted Container Security, Nessus

Risk Information

VPR

Risk Factor: Low

Score: 3

Percentile: 23.63

CVSS v2

Risk Factor: Low

Base Score: 2.6

Temporal Score: 1.9

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

CVSS Score Source: CVE-2026-80213

CVSS v3

Risk Factor: Medium

Base Score: 4

Temporal Score: 3.5

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

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

Vulnerability Information

CPE: cpe:/o:amazon:linux:2023, p-cpe:/a:amazon:linux:ruby4.0-bundled-gems-debuginfo, p-cpe:/a:amazon:linux:ruby4.0-bundled-gems, p-cpe:/a:amazon:linux:ruby4.0-debuginfo, p-cpe:/a:amazon:linux:ruby4.0-debugsource, p-cpe:/a:amazon:linux:ruby4.0-default-gems, p-cpe:/a:amazon:linux:ruby4.0-devel, p-cpe:/a:amazon:linux:ruby4.0-doc, p-cpe:/a:amazon:linux:ruby4.0-libs-debuginfo, p-cpe:/a:amazon:linux:ruby4.0-libs, p-cpe:/a:amazon:linux:ruby4.0-rubygem-bigdecimal-debuginfo, p-cpe:/a:amazon:linux:ruby4.0-rubygem-bigdecimal, p-cpe:/a:amazon:linux:ruby4.0-rubygem-bundler, p-cpe:/a:amazon:linux:ruby4.0-rubygem-io-console-debuginfo, p-cpe:/a:amazon:linux:ruby4.0-rubygem-io-console, p-cpe:/a:amazon:linux:ruby4.0-rubygem-irb, p-cpe:/a:amazon:linux:ruby4.0-rubygem-json-debuginfo, p-cpe:/a:amazon:linux:ruby4.0-rubygem-json, p-cpe:/a:amazon:linux:ruby4.0-rubygem-minitest, p-cpe:/a:amazon:linux:ruby4.0-rubygem-power_assert, p-cpe:/a:amazon:linux:ruby4.0-rubygem-psych-debuginfo, p-cpe:/a:amazon:linux:ruby4.0-rubygem-psych, p-cpe:/a:amazon:linux:ruby4.0-rubygem-racc-debuginfo, p-cpe:/a:amazon:linux:ruby4.0-rubygem-racc, p-cpe:/a:amazon:linux:ruby4.0-rubygem-rake, p-cpe:/a:amazon:linux:ruby4.0-rubygem-rbs-debuginfo, p-cpe:/a:amazon:linux:ruby4.0-rubygem-rbs, p-cpe:/a:amazon:linux:ruby4.0-rubygem-rdoc, p-cpe:/a:amazon:linux:ruby4.0-rubygem-rexml, p-cpe:/a:amazon:linux:ruby4.0-rubygem-rss, p-cpe:/a:amazon:linux:ruby4.0-rubygem-test-unit, p-cpe:/a:amazon:linux:ruby4.0-rubygem-typeprof, p-cpe:/a:amazon:linux:ruby4.0-rubygems-devel, p-cpe:/a:amazon:linux:ruby4.0-rubygems, p-cpe:/a:amazon:linux:ruby4.0

Required KB Items: Host/local_checks_enabled, Host/AmazonLinux/release, Host/AmazonLinux/rpm-list

Exploit Ease: No known exploits are available

Patch Publication Date: 9/14/2026

Vulnerability Publication Date: 8/27/2026

Reference Information

CVE: CVE-2026-80212, CVE-2026-80213