Pierluigi Paganini August 30, 2023

Threat actors started using the exploit chain in attacks on Juniper EX switches and SRX firewalls shortly after the release of the PoC code.

This week, watchTowr Labs security researchers published a proof-of-concept exploit (PoC) exploit code for vulnerabilities in Juniper SRX firewalls. An unauthenticated attacker can chain the vulnerabilities to gain remote code execution in Juniper JunOS on vulnerable devices.

In mid-August, Juniper addressed four medium-severity (CVSS 5.3) vulnerabilities (CVE-2023-36844, CVE-2023-36845, CVE-2023-36846, CVE-2023-36847) impacting EX switches and SRX firewalls.

The vulnerabilities reside in the J-Web component of Juniper Networks Junos OS on SRX Series and EX Series.

“Multiple vulnerabilities in the J-Web component of Juniper Networks Junos OS on SRX Series and EX Series have been resolved through the application of specific fixes to address each vulnerability.” reads the advisory published by Juniper. “By chaining exploitation of these vulnerabilities, an unauthenticated, network-based attacker may be able to remotely execute code on the devices.”

“With a specific request that doesn’t require authentication an attacker is able to upload arbitrary files via J-Web, leading to a loss of integrity for a certain part of the file system, which may allow chaining to other vulnerabilities,” says Juniper.

The company also suggests disabling J-Web, or limiting access to only trusted hosts, as a workaround for this flaw.

watchTowr Labs security researchers exploited a pre-authentication upload vulnerability (CVE-2023-36846) to upload an arbitrary PHP file to a restricted directory with a randomised file name. Then they exploited the same vulnerable function to upload a PHP configuration file (.ini) which points to and loads the above PHP file using the auto_prepend_file directive.

As all environment variables can be set via HTTP requests, the researchers exploited the CVE-2023-36845 to overwrite the environment variable PHPRC and load the PHP configuration file and trigger the execution of the PHP file initially uploaded.

watchTowr also published a deep dive into reproducing, chaining and exploiting these vulnerabilities.

“This is an interesting bug chain, utilising two bugs that would be near-useless in isolation and combining them for a ‘world ending’ unauthenticated RCE.” explained the researchers.

“Given the simplicity of exploitation, and the privileged position that JunOS devices hold in a network, we would not be surprised to see large-scale exploitation.” continues the experts.

Shadowserver Foundation researchers started observing threat actors chaining the recently disclosed flaws in Juniper EX switches and SRX firewalls in attacks against devices exposed online.

“Since 25th August we are seeing exploitation attempts from multiple IPs for Juniper J-Web CVE-2023-36844 (& friends) targeting /webauth_operation.php endpoint. Same day an exploit POC was published.” warns the Shadowserver Foundation.

The researchers are currently tracking over 8200 IPs with exposed J-Web interfaces, most of them in South Korea followed by the United States.

BleepingComputer reported that according to Shadowserver CEO Piotr Kijewski, threat actors are using exploits based on the watchTowr Labs’ PoC.

According to Kijewski, the explotation attempts originated from at least 29 IPs, likely from different threat actors.

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Pierluigi Paganini

(SecurityAffairs – hacking, Juniper)