← Vulnerability feed

Vulnerability record · CVE-2021-31354 · published 19 October 2021

CVE-2021-31354: Juniper junos out-of-bounds read vulnerability

Juniper · Junos

An Out Of Bounds (OOB) access vulnerability in the handling of responses by a Juniper Agile License (JAL) Client in Juniper Networks Junos OS and Junos OS Evolved, configured in Network Mode (to use Juniper Agile License Manager) may allow an attacker to cause a partial Denial of Service (DoS), or lead to remote code execution (RCE). The vulnerability exists in the packet parsing logic on the client that processes the response from the server using a custom protocol. An attacker with control of a JAL License Manager, or with access to the local broadcast domain, may be able to spoof a new JAL License Manager and/or craft a response to the Junos OS License Client, leading to exploitation of this vulnerability. This issue only affects Junos systems configured in Network Mode. Systems that are configured in Standalone Mode (the default mode of operation for all systems) are not vulnerable to this issue. This issue affects: Juniper Networks Junos OS: 19.2 versions prior to 19.2R3-S3; 19.3 versions prior to 19.3R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3-S1; 20.2 versions prior to 20.2R3-S2; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R3; 21.1 versions prior to 21.1R2. Juniper Networks Junos OS Evolved: version 20.1R1-EVO and later versions, prior to 21.2R2-EVO. This issue does not affect Juniper Networks Junos OS versions prior to 19.2R1.

8.8 CVSS 3.1 High EPSS 0.63% · top 51.9% CWE-125 · Out-of-bounds read
8.8CVSS 3.1 base score, v2 5.4
0.63%EPSS exploitation probability, 30 days
NoNot in CISA KEV
2Affected product versions listed by NVD
2References
17 Jun 2026Last modified by NVD

Description

An Out Of Bounds (OOB) access vulnerability in the handling of responses by a Juniper Agile License (JAL) Client in Juniper Networks Junos OS and Junos OS Evolved, configured in Network Mode (to use Juniper Agile License Manager) may allow an attacker to cause a partial Denial of Service (DoS), or lead to remote code execution (RCE). The vulnerability exists in the packet parsing logic on the client that processes the response from the server using a custom protocol. An attacker with control of a JAL License Manager, or with access to the local broadcast domain, may be able to spoof a new JAL License Manager and/or craft a response to the Junos OS License Client, leading to exploitation of this vulnerability. This issue only affects Junos systems configured in Network Mode. Systems that are configured in Standalone Mode (the default mode of operation for all systems) are not vulnerable to this issue. This issue affects: Juniper Networks Junos OS: 19.2 versions prior to 19.2R3-S3; 19.3 versions prior to 19.3R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3-S1; 20.2 versions prior to 20.2R3-S2; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R3; 21.1 versions prior to 21.1R2. Juniper Networks Junos OS Evolved: version 20.1R1-EVO and later versions, prior to 21.2R2-EVO. This issue does not affect Juniper Networks Junos OS versions prior to 19.2R1.

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

2 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://kb.juniper.net/JSA11219 Vendor Advisory
https://kb.juniper.net/JSA11219 Vendor Advisory

Track CVE-2021-31354 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

Start free Open in platform

Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2023-36845Juniper Junos OS J-Web PHP variable modification RCEJ-Web in Junos OS on EX Series and SRX Series mishandles the PHP PHPRC environment variable, letting a crafted request alter the PHP execution enviro…KEVEPSS 95%analysed9.8CVE-2020-1631Juniper Junos OS J-Web HTTP service path traversal and local file inclusionThe HTTP/HTTPS service behind J-Web, Web Authentication, Dynamic-VPN, Firewall Authentication Pass-Through with Web-Redirect, and ZTP in Junos OS doe…KEVEPSS 4.8%analysed6.7CVE-2025-21590Juniper Junos OS kernel improper isolation allows local code injectionJunos OS contains an improper isolation or compartmentalization flaw in the kernel that lets a local attacker with shell access inject arbitrary code…KEVEPSS 1.7%analysed5.3CVE-2023-36851Juniper Junos OS SRX J-Web missing authentication allows file upload/downloadJunos OS on SRX Series exposes webauth_operation.php without authentication, letting a network attacker upload and download arbitrary files through J…KEVEPSS 1.1%analysed5.3CVE-2023-36844Juniper Junos OS EX Series J-Web PHP Environment Variable ModificationJ-Web on Junos OS for EX Series fails to properly restrict external PHP variable modification, letting an unauthenticated network attacker alter impo…KEVEPSS 90%analysed5.3CVE-2023-36846Juniper Junos OS SRX J-Web Missing Authentication Allows File UploadJunos OS on SRX Series fails to require authentication for a critical function in user.php reachable through J-Web, letting an unauthenticated networ…KEVEPSS 93%analysed5.3CVE-2023-36847Juniper Junos OS EX Series J-Web installAppPackage.php missing authenticationJunos OS on EX Series exposes installAppPackage.php through J-Web without requiring authentication. An unauthenticated network attacker can upload ar…KEVEPSS 83%analysed10.0CVE-2021-31384Juniper junos improper authorization vulnerabilityDue to a Missing Authorization weakness and Insufficient Granularity of Access Control in a specific device configuration, a vulnerability exists in …EPSS 1.2%

Source: NIST National Vulnerability Database (record CVE-2021-31354), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.