CVE-2023-36844: Juniper Junos OS EX Series PHP External Variable Modification Vulnerability

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Yes, if you run Juniper Junos OS. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2023-11-13, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2023-11-17; treat that as the outer limit, not the target.
• EPSS 90.0%, percentile 99.8: FIRST’s model estimates a 90.0% chance of exploitation activity in the next 30 days, higher than 99.8% of all scored CVEs (very high). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.

What it is

A PHP External Variable Modification vulnerability in J-Web of Juniper Networks Junos OS on EX Series allows an unauthenticated, network-based attacker to control certain, important environment variables. Using a crafted request an attacker is able to modify certain PHP environment variables leading to partial loss of integrity, which may allow chaining to other vulnerabilities. This issue affects Juniper Networks Junos OS on EX Series: All versions prior to 20.4R3-S9; 21.1 versions 21.1R1 and later; 21.2 versions prior to 21.2R3-S7; 21.3 versions prior to 21.3R3-S5; 21.4 versions prior to 21.4R3-S5; 22.1 versions prior to 22.1R3-S4; 22.2 versions prior to 22.2R3-S2; 22.3 versions prior to 22.3R3-S1; 22.4 versions prior to 22.4R2-S2, 22.4R3; 23.2 versions prior to 23.2R1-S1, 23.2R2.

CISA’s summary

Juniper Junos OS on EX Series contains a PHP external variable modification vulnerability that allows an unauthenticated, network-based attacker to control certain, important environment variables. Using a crafted request an attacker is able to modify certain PHP environment variables, leading to partial loss of integrity, which may allow chaining to other vulnerabilities.

Weakness type: CWE-473.

Product: Juniper Junos OS · Assigned by: juniper · Published: 2023-08-17

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: added 2023-11-13; federal due date 2023-11-17. Known ransomware use: Unknown.
• CISA required action: Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
• CISA SSVC assessment: exploitation active, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 89.96% probability of exploitation activity in the next 30 days; percentile 99.8.

Timeline

• 2023-08-17 — CVE record published by juniper
• 2023-11-13 — Added to CISA’s Known Exploited Vulnerabilities catalog
• 2023-11-17 — CISA remediation deadline for US federal agencies
• 2025-10-21 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. supportportal.juniper.net supportportal.juniper.net
2. Listed in CISA KEV notes (supportportal.juniper.net) supportportal.juniper.net

Vulnerability records

1. CVE.org record CVE-2023-36844 cve.org
2. NVD entry CVE-2023-36844 nvd.nist.gov

Government

1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov

Other references from the CVE record and advisory

1. packetstormsecurity.com packetstormsecurity.com

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