A flaw was found in gnutls. Servers configured with RSA-PSK (Rivest–Shamir–Adleman – Pre-Shared Key) wrongfully matched usernames containing a NUL character with truncated usernames. A remote attacker could exploit this by sending a specially crafted username, leading to an authentication bypass. This vulnerability allows an attacker to gain unauthorized access by circumventing the authentication process.

An update of the gnutls package has been released.

The remote Ubuntu 22.04 LTS / 24.04 LTS / 25.10 / 26.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8284-1 advisory.

    Joshua Rogers discovered that GnuTLS did not properly handle malformed DTLS handshake fragments in certain     cases. A remote attacker could possibly use this issue to obtain sensitive information, or cause a denial     of service. (CVE-2026-33845)

    Haruto Kimura, Oscar Reparaz, and Zou Dikai discovered that GnuTLS did not properly validate DTLS     handshake fragment lengths in certain cases. A remote attacker could possibly use this issue to cause     GnuTLS to crash, resulting in a denial of service, or execute arbitrary code. (CVE-2026-33846)

    Oleh Konko and Joshua Rogers discovered that GnuTLS did not properly validate OCSP responses in certain     cases. A remote attacker could possibly use this issue to bypass certificate revocation checks, leading to     a machine-in-the-middle attack. (CVE-2026-3832)

    Oleh Konko and Joshua Rogers discovered that GnuTLS did not properly handle case-insensitive name     constraints in certain cases. A remote attacker could possibly use this issue to bypass certificate     validation, leading to a machine-in-the-middle attack. (CVE-2026-3833)

    Joshua Rogers discovered that GnuTLS did not properly order DTLS packets with duplicate sequence numbers     in certain cases. A remote attacker could possibly use this issue to cause GnuTLS to crash, resulting in a     denial of service. (CVE-2026-42009)

    Joshua Rogers discovered that GnuTLS did not properly handle usernames containing NUL characters in     certain RSA-PSK configurations. A remote attacker could possibly use this issue to bypass authentication     and gain unintended access to services. (CVE-2026-42010)

    Haruto Kimura discovered that GnuTLS did not properly apply permitted name constraints in certain     certificate validation paths. A remote attacker could possibly use this issue to bypass certificate     validation, leading to a machine-in-the-middle attack. (CVE-2026-42011)

    Oleh Konko discovered that GnuTLS incorrectly fell back to Common Name checks for certain URI and SRV     subject alternative names. A remote attacker could possibly use this issue to bypass certificate     validation, leading to a machine-in-the-middle attack. (CVE-2026-42012)

    Haruto Kimura and Joshua Rogers discovered that GnuTLS incorrectly fell back to Common Name checks when     subject alternative names were oversized. A remote attacker could possibly use this issue to bypass     certificate validation, leading to a machine-in-the-middle attack. (CVE-2026-42013)

    Luigino Camastra and Joshua Rogers discovered that GnuTLS had a use-after-free issue when changing PKCS#11     token security officer PINs in certain cases. An attacker could possibly use this issue to cause GnuTLS to     crash, resulting in a denial of service, or execute arbitrary code. (CVE-2026-42014)

    Zou Dikai discovered that GnuTLS did not properly validate PKCS#12 bag sizes in certain cases. An attacker     could possibly use this issue to cause GnuTLS to crash, resulting in a denial of service, or execute     arbitrary code. (CVE-2026-42015)

    Joshua Rogers discovered that GnuTLS did not properly handle very short premaster secrets in certain RSA     key exchange cases with PKCS#11-backed server keys. A remote attacker could possibly use this issue to     obtain sensitive information. (CVE-2026-5260)

    Doria Tang discovered that GnuTLS did not perform PKCS#7 padding checks in constant time in certain cases.
    A remote attacker could possibly use this issue to obtain sensitive information. This issue only affected     Ubuntu 24.04 LTS, Ubuntu 25.10, and Ubuntu 26.04 LTS. (CVE-2026-5419)

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.

The remote Debian 12 / 13 host has packages installed that are affected by multiple vulnerabilities as referenced in the dsa-6281 advisory.

    - -------------------------------------------------------------------------     Debian Security Advisory DSA-6281-1                   security@debian.org     https://www.debian.org/security/                     Salvatore Bonaccorso     May 19, 2026                          https://www.debian.org/security/faq
    - -------------------------------------------------------------------------

    Package        : gnutls28     CVE ID         : CVE-2026-3832 CVE-2026-3833 CVE-2026-5260 CVE-2026-5419                      CVE-2026-33845 CVE-2026-33846 CVE-2026-42009 CVE-2026-42010                      CVE-2026-42011 CVE-2026-42012 CVE-2026-42013 CVE-2026-42014                      CVE-2026-42015     Debian Bug     : 1135319

    Multiple security vulnerabilities have been discovered in GnuTLS, a     library implementing the TLS and SSL protocols, which may result in     execution of arbitrary code, denial of service, information leak,     certificate misuse, name constraint bypass, authentication bypass,     revocation bypass or timing side-channel attacks.

    For the oldstable distribution (bookworm), these problems have been     fixed in version 3.7.9-2+deb12u7.

    For the stable distribution (trixie), these problems have been fixed in     version 3.8.9-3+deb13u4.

    We recommend that you upgrade your gnutls28 packages.

    For the detailed security status of gnutls28 please refer to its     security tracker page at:
    https://security-tracker.debian.org/tracker/gnutls28

    Further information about Debian Security Advisories, how to apply     these updates to your system and frequently asked questions can be     found at: https://www.debian.org/security/

    Mailing list: debian-security-announce@lists.debian.org

Tenable has extracted the preceding description block directly from the Debian 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 remote CentOS Linux 9 host has packages installed that are affected by multiple vulnerabilities as referenced in the gnutls-3.8.10-4.el9 build changelog.

  - A flaw was found in gnutls. This vulnerability occurs because gnutls performs case-sensitive comparisons     of `nameConstraints` labels, specifically for `dNSName` (DNS) or `rfc822Name` (email) constraints within     `excludedSubtrees` or `permittedSubtrees`. A remote attacker can exploit this by crafting a leaf     certificate with casing differences in the Subject Alternative Name (SAN), leading to a policy bypass     where a certificate that should be rejected is instead accepted. This could result in unauthorized access     or information disclosure. (CVE-2026-3833)

  - A flaw was found in the GnuTLS library, specifically in the gnutls_pkcs11_token_init() function that     handles PKCS#11 token initialization. When a token label longer than expected is processed, the function     writes past the end of a fixed-size stack buffer. This programming error can cause the application using     GnuTLS to crash or, in certain conditions, be exploited for code execution. As a result, systems or     applications relying on GnuTLS may be vulnerable to a denial of service or local privilege escalation     attacks. (CVE-2025-9820)

  - A flaw in GnuTLS DTLS handshake parsing allows malformed fragments with zero length and non-zero offset,     leading to an integer underflow during reassembly and resulting in an out-of-bounds read. This issue is     remotely exploitable and may cause information disclosure or denial of service. (CVE-2026-33845)

  - A heap buffer overflow vulnerability exists in the DTLS handshake fragment reassembly logic of GnuTLS. The     issue arises in merge_handshake_packet() where incoming handshake fragments are matched and merged based     solely on handshake type, without validating that the message_length field remains consistent across all     fragments of the same logical message. An attacker can exploit this by sending crafted DTLS fragments with     conflicting message_length values, causing the implementation to allocate a buffer based on a smaller     initial fragment and subsequently write beyond its bounds using larger, inconsistent fragments. Because     the merge operation does not enforce proper bounds checking against the allocated buffer size, this     results in an out-of-bounds write on the heap. The vulnerability is remotely exploitable without     authentication via the DTLS handshake path and can lead to application crashes or potential memory     corruption. (CVE-2026-33846)

  - A flaw was found in gnutls. A remote attacker could exploit this vulnerability by presenting a specially     crafted Online Certificate Status Protocol (OCSP) response during a TLS handshake. Due to a logic error in     how gnutls processes multi-record OCSP responses, a client with OCSP verification enabled may incorrectly     accept a revoked server certificate, potentially leading to a compromise of trust. (CVE-2026-3832)

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.

  - A flaw was found in gnutls. Servers configured with RSA-PSK (RivestShamirAdleman  Pre-Shared Key)     wrongfully matched usernames containing a NUL character with truncated usernames. A remote attacker could     exploit this by sending a specially crafted username, leading to an authentication bypass. This     vulnerability allows an attacker to gain unauthorized access by circumventing the authentication process.
    (CVE-2026-42010)

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

ID	Name	Product	Family	Severity
316057	Photon OS 4.0: Gnutls PHSA-2026-4.0-1016	Nessus	PhotonOS Local Security Checks	critical
316043	Ubuntu 22.04 LTS / 24.04 LTS / 25.10 / 26.04 LTS : GnuTLS vulnerabilities (USN-8284-1)	Nessus	Ubuntu Local Security Checks	critical
315514	Debian dsa-6281 : gnutls-bin - security update	Nessus	Debian Local Security Checks	critical
312106	CentOS 9 : gnutls-3.8.10-4.el9	Nessus	CentOS Local Security Checks	critical
311253	Linux Distros Unpatched Vulnerability : CVE-2026-42010	Nessus	Misc.	critical

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