How to Fix CVE-2023-36844: PHP External Variable Modification in Juniper Networks Junos OS

By Sai Kiran Pandrala

This advisory bundle also covers: CVE-2023-36846, CVE-2023-36847, CVE-2023-36851. The patched build below closes all sibling CVEs in the same vendor release.

What is CVE-2023-36844?

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 versi

A successful exploit gives the remote attacker the impact described in the vendor advisory. The fix is to install the patched build from Juniper Networks listed in the table above and confirm the running version after the upgrade.

Am I affected?

Check your installed version of Juniper Networks Junos OS against the Affected row above. If your build sits within any of those ranges, treat the system as vulnerable until patched.

If you do not have the version handy, pull it the same way you usually would for Junos OS: the management console's About page, the CLI's version command, or the package manager record for the installed binary. The vendor advisory linked in the references section is the authoritative source.

How to fix CVE-2023-36844

1. Read the vendor advisory at https://supportportal.juniper.net/JSA72300 for the build matrix that matches your installation.
2. Identify the patched build for your major version: Junos OS: 20.4R3-S9, 21.1, 21.2R3-S6, 21.3R3-S5, 21.4R3-S5, 22.1R3-S4, 22.2R3-S2, 22.3R3-S1, 22.4R2-S2, 23.2R1-S1.
3. Back up configuration before upgrading (export running config, snapshot the VM, or take a database dump as appropriate for your platform).
4. Apply the patched build using the vendor's documented upgrade path (in-place upgrade, package update, or replacement image).
5. Restart the service so the new code is loaded; verify the running version reports the patched build number.

Upgrade Junos to the patched release

# Verify the running Junos build
show version

# Stage the patched Junos image from the advisory: https://supportportal.juniper.net/JSA72300
request system software add /var/tmp/jinstall-<patched-version>-signed.tgz no-validate reboot

# After reboot
show version

Verify the fix landed

# 1. Confirm the running version matches the fixed-in version from the advisory:
#    https://supportportal.juniper.net/JSA72300
#    Use the platform-specific version probe above.

# 2. Re-scan with your vulnerability scanner (Nessus, Qualys, Tenable, OpenVAS).
#    The scanner should no longer flag CVE-2023-36844 on the patched target.

# 3. Inspect recent service / kernel logs for crash loops or rollback events.
journalctl -u <service> --since "10 minutes ago"
dmesg --since "10 minutes ago"

If you can't patch immediately

Check the vendor advisory's "Workarounds" section. If the advisory lists no official workaround, patching is the only remediation. Compensating controls that reduce attack surface in the meantime: restrict network access to the management interface to a small admin allowlist, disable the affected feature if it is not in use, and monitor the relevant logs for the exploitation patterns referenced in the advisory.

How to verify the fix worked

1. Confirm the running version matches the patched build from the vendor advisory.
2. Re-run your vulnerability scanner; the CVE should clear.
3. Review logs from before the patch for the exploitation signatures described in the advisory, and treat any matches as a possible compromise (rotate credentials, isolate the host, full IR).

Frequently asked questions

Is CVE-2023-36844 being exploited right now?

Yes. It is listed in the CISA Known Exploited Vulnerabilities catalog (added 2023-11-13), which means CISA has evidence of active exploitation.

What is the CVSS score for CVE-2023-36844?

CVSS 5.3 (Medium). Use this with your own asset exposure to set patching priority (internet-exposed systems first).

Do I need to take the system offline to patch?

It depends on the platform. Many appliances support hitless upgrade in HA pairs (upgrade standby, fail over, upgrade primary). Servers and applications usually need a service restart. Plan a maintenance window if HA is not available.

What if my version is not listed as affected?

Cross-check against the vendor advisory linked below. The CVE record reflects the vendor's official affected-products list at publication time; later-discovered variants are added through the same advisory or a follow-up CVE.

References

• Official vendor advisory: https://supportportal.juniper.net/JSA72300
• NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-36844
• CISA KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• http://packetstormsecurity.com/files/174865/Juniper-SRX-Firewall-EX-Switch-Remote-Code-Execution.html

*This guide was assembled from the official vendor advisory, NVD record, and CISA KEV listing on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*