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.

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.

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.

  - 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)

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

The remote SUSE Linux SLED15 / SLED_SAP15 / SLES15 / SLES_SAP15 host has packages installed that are affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:1066-1 advisory.

    - CVE-2024-49761: ReDoS vulnerability in REXML gem (bsc#1232440 bsc#1232441).
    - CVE-2025-58767: denial of service when parsing XML containing multiple XML declarations (bsc#1250016).
    - CVE-2026-27820: insufficient checks in `zstream_buffer_ungets` can lead to a buffer overflow     (bsc#1259239).

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

Note that Nessus has not tested for these issues 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:

  - 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)

ID	Name	Product	Family	Severity
327617	Ubuntu 16.04 LTS : Ruby vulnerabilities (USN-8556-1)	Nessus	Ubuntu 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
306840	Linux Distros Unpatched Vulnerability : CVE-2026-27820	Nessus	Misc.	medium
303945	SUSE SLED15 / SLES15 Security Update : ruby2.5 (SUSE-SU-2026:1066-1)	Nessus	SuSE Local Security Checks	high
438901	Alpine: multiple ruby packages: security update to 3.4.9-r0	Tenable Cloud Security	Alpine Linux Local Security Checks	medium
438901	Alpine: multiple ruby packages: security update to 3.4.9-r0	Tenable Self-Hosted Container Security	Alpine Linux Local Security Checks	medium

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