Detections
Analytics

Linux Distros Unpatched Vulnerability : CVE-2026-84308

medium Nessus Plugin ID 342554

Language:

Synopsis

The Linux/Unix host has one or more packages installed with a vulnerability that the vendor indicates will not be patched.

Description

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

 - phpseclib is a PHP secure communications library. Prior to 3.0.57 and 4.0.1, pure-PHP X25519 scalar multiplication in phpseclib/Math/PrimeField/Integer.php performs data-dependent conditional modular reductions in add() and subtract(). During the Montgomery ladder in phpseclib/Crypt/EC/BaseCurves/Montgomery.php, the reduction behavior of each step depends on the secret scalar prefix, creating per-step timing and libgmp call-count observations that can reveal a reused 251-bit clamped private scalar. The phpseclib/Crypt/EC/Formats/Keys/MontgomeryPrivate.php derivation path invokes the pure-PHP multiplication without a native-engine check, while phpseclib/Crypt/EC/Formats/Keys/PKCS8.php reaches it when ext-sodium is unavailable. Exploitation requires a reused or long-lived X25519 private key, knowledge of the corresponding public key, execution of the pure-PHP path, and a local observer capable of resolving individual ladder steps or libgmp entry-point calls. Ephemeral X25519 keys, including phpseclib's normal SSH exchange path, are not affected. Recovery of the scalar permanently compromises operations that reuse that key. This issue is fixed in versions 3.0.57 and 4.0.1. (CVE-2026-84308)

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

Solution

There is no known solution at this time.

See Also

https://security-tracker.debian.org/tracker/CVE-2026-84308

https://ubuntu.com/security/CVE-2026-84308

Plugin Details

Severity: Medium

ID: 342554

File Name: unpatched_CVE_2026_84308.nasl

Version: 1.1

Type: Local

Agent: unix

Family: Misc.

Published: 9/3/2026

Updated: 9/3/2026

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

Risk Information

VPR

Risk Factor: Medium

Score: 4.3

Percentile: 53.46

CVSS v2

Risk Factor: Medium

Base Score: 4.3

Temporal Score: 3.7

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

CVSS Score Source: CVE-2026-84308

CVSS v3

Risk Factor: Medium

Base Score: 6.3

Temporal Score: 5.8

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

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

Vulnerability Information

CPE: cpe:/o:canonical:ubuntu_linux:14.04:-:lts, cpe:/o:canonical:ubuntu_linux:16.04:-:lts, cpe:/o:canonical:ubuntu_linux:18.04:-:lts, cpe:/o:canonical:ubuntu_linux:20.04:-:lts, cpe:/o:canonical:ubuntu_linux:22.04:-:lts, cpe:/o:canonical:ubuntu_linux:24.04:-:lts, cpe:/o:canonical:ubuntu_linux:26.04:-:lts, cpe:/o:debian:debian_linux:12.0, cpe:/o:debian:debian_linux:13.0, p-cpe:/a:canonical:ubuntu_linux:php5, p-cpe:/a:canonical:ubuntu_linux:php7.2, p-cpe:/a:canonical:ubuntu_linux:php7.4, p-cpe:/a:canonical:ubuntu_linux:php8.1, p-cpe:/a:canonical:ubuntu_linux:php8.3, p-cpe:/a:canonical:ubuntu_linux:php8.5, p-cpe:/a:canonical:ubuntu_linux:phpseclib, p-cpe:/a:debian:debian_linux:php-phpseclib3

Required KB Items: Host/local_checks_enabled, Host/cpu, global_settings/vendor_unpatched, Host/OS/identifier

Exploit Ease: No known exploits are available

Vulnerability Publication Date: 9/1/2026

Reference Information

CVE: CVE-2026-84308