Security researchers have uncovered a highly critical remote code execution (RCE) vulnerability in Juniper Networks’ firewalls, routers, and switches that could allow attackers to take full control of affected devices. Juniper has released patches to address the flaw, tracked as CVE-2024-21591.
Technical Details of the Vulnerability
The vulnerability resides in the Junos OS SNMP poller daemon which listens on TCP and UDP port 161 for incoming SNMP requests. Researchers from SOC Prime discovered that the daemon contains an input validation flaw that enables malicious actors to send specially crafted SNMP packets to trigger remote code execution.
Specifically, the issue stems from improper handling of the PDU length field value in SNMP request packets. By supplying an overly large value in the length field, an attacker can trigger a heap buffer overflow condition that overwrites adjacent memory and hijacks control flow to execute arbitrary commands with elevated privileges on the underlying FreeBSD operating system powering Juniper’s network gear.
The table below summarizes the key details regarding CVE-2024-21591:
|Network / Adjacent Network
|Junos OS SNMP poller daemon
|Firewalls, routers, switches
Gaining remote access in this manner would allow perpetrators to steal sensitive information, carry out network reconnaissance, and pivot to further compromise critical systems.
Widespread Impact Across Juniper Product Lines
The underlying vulnerability affects dozens of hardware and virtualized models across Juniper’s security, routing, and switching product portfolios. According to Juniper’s security advisory, vulnerable devices include:
- SRX Series Services Gateways
- vSRX Virtual Firewalls
- J-Series and T-Series Routers
- ACX and PTX Series Routers
- MX Series 5G Universal Routing Platform
- EX Series Ethernet Switches
And various other devices. Essentially, any equipment running Junos OS with the SNMP daemon enabled is potentially vulnerable if left unpatched.
Juniper’s Mitigations and Patches
Upon discovering the remotely exploitable bug, Juniper promptly released patched versions of Junos OS to eliminate the flaw:
Junos OS Release 32.0R3 on January 14th, 2024
Followed by Junos OS Releases 21.4R3, 19.4R4, and 17.4R3 on January 15th, 2024
Juniper has urged customers to upgrade devices to the latest patched releases as soon as possible.
As a temporary risk mitigation, administrators can disable the SNMP poller daemon (
snmpd) on firewalls, routers, and switches connected directly to untrusted networks. However this workaround is only recommended for devices that do not rely on SNMP for monitoring and management.
Although CVSS rates the vulnerability as “low complexity”, attackers would only need to send specially formatted input via SNMP to trigger the heap buffer overflow. No authentication is required to exploit the flaw remotely.
Once the heap corruption has occurred, additional techniques would be needed to control code execution such as preparation of the payload, defeating exploit mitigations, etc. But the primary vulnerability activation process itself is straightforward.
And since SNMP uses UDP, packets can be sent from spoofed IP addresses, making the attack relatively easy to obfuscate.
Potential for Wormable Exploits
The far reach of the vulnerability across Juniper’s vast customer base means that worms or other malware could propagate automatically from device to device once an exploit becomes publicly available.
Similar to the infamous Conficker worm that spread via a Windows RPC vulnerability in the late 2000s, malware authors could target CVE-2024-21591 to infect hundreds of thousands of devices in a short period.
Outlook and Conclusions
With remote code execution flaws as severe as this now in the public domain, administrators should immediately assess their exposure and apply the necessary Junos OS updates to avoid potential compromise.
The next few weeks are critical since weaponized exploits may emerge in various hacking forums or dark web marketplaces. So time is of the essence – upgrading should be treated as an utmost priority.
While Juniper’s response has been swift and transparent, the underlying bug highlights greater systemic issues related to input validation and memory safety that continue to plague embedded devices and software written in unsafe languages like C/C++.
Until more fundamental security practices take hold, dangerous code execution bugs will persist as low-hanging fruit for attackers and cannot be considered rare “zero-day” occurrences anymore. A new approach emphasizing attack resistance alongside detection and response is desperately needed.
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