CVE-2021-0249 in Junos OS
Summary
by MITRE • 04/23/2021
On SRX Series devices configured with UTM services a buffer overflow vulnerability in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS may allow an attacker to arbitrarily execute code or commands on the target to take over or otherwise impact the device by sending crafted packets to or through the device. This issue affects: Juniper Networks Junos OS on SRX Series: 15.1X49 versions prior to 15.1X49-D190; 17.4 versions prior to 17.4R2-S9; 17.4R3 and later versions prior to 18.1R3-S9; 18.2 versions prior to 18.2R3-S1; 18.3 versions prior to 18.3R2-S3, 18.3R3; 18.4 versions prior to 18.4R2-S3, 18.4R3; 19.1 versions prior to 19.1R1-S4, 19.1R2; 19.2 versions prior to 19.2R1-S1, 19.2R2. An indicator of compromise can be the following text in the UTM log: RT_UTM: AV_FILE_NOT_SCANNED_PASSED_MT:
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Analysis
by VulDB Data Team • 04/29/2021
This buffer overflow vulnerability exists within the Packet Forwarding Engine of Juniper Networks SRX Series devices running specific Junos OS versions. The flaw occurs when processing crafted packets through UTM services, creating a condition where attacker-controlled data can overwrite adjacent memory locations in the PFE component. The vulnerability stems from insufficient input validation and bounds checking in the packet processing pipeline, allowing maliciously constructed packets to trigger memory corruption that can be exploited for arbitrary code execution. The issue specifically impacts devices configured with Unified Threat Management services, making it particularly dangerous for network security appliances that handle extensive traffic processing. The vulnerability allows remote attackers to gain control over the affected device, potentially leading to complete system compromise and unauthorized access to network resources. The affected versions span multiple Junos OS release lines including 15.1X49, 17.4, 18.2, 18.3, 18.4, 19.1, and 19.2, indicating a widespread impact across several software branches.
The technical exploitation of this vulnerability follows a classic buffer overflow attack pattern where attacker-controlled input data exceeds the allocated buffer size in the PFE memory space. When the device processes malicious packets through UTM services, the insufficient bounds checking allows data to overwrite critical memory regions including return addresses and function pointers. This memory corruption can be leveraged to redirect execution flow to attacker-controlled code, enabling remote command execution with the privileges of the affected process. The specific log indicator RT_UTM: AV_FILE_NOT_SCANNED_PASSED_MT suggests that the attack may be triggered through file scanning operations within the UTM framework, where crafted packets bypass normal security checks and cause the buffer overflow condition. This pattern aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a direct threat to the integrity and availability of network security infrastructure.
The operational impact of this vulnerability extends beyond simple system compromise to encompass complete network infrastructure disruption and potential data breaches. An attacker who successfully exploits this vulnerability can gain root-level access to the SRX device, allowing them to modify firewall rules, disable security services, monitor network traffic, and potentially pivot to other network segments. The remote execution capability means that attackers do not require physical access or network proximity to exploit the vulnerability, making it particularly dangerous for perimeter security devices. Organizations relying on SRX Series appliances for network protection face significant risk of unauthorized access to their protected networks, potentially leading to data exfiltration, service disruption, and compliance violations. The vulnerability affects critical network infrastructure components, making it a high-priority target for threat actors seeking to establish persistent access to enterprise networks.
Mitigation strategies for this vulnerability should include immediate patching of affected Junos OS versions to the recommended secure releases, as outlined in Juniper's security advisory. Network administrators should implement network segmentation and monitoring to detect suspicious packet patterns that may indicate exploitation attempts. The implementation of intrusion detection systems with signature-based detection for the specific log indicators mentioned in the vulnerability description can help identify potential attacks. Organizations should also consider deploying network access controls to limit exposure of affected devices to untrusted networks and implement proper logging and monitoring of UTM services to detect anomalous behavior. Additionally, network security teams should review and update their incident response procedures to account for potential exploitation of this vulnerability, ensuring rapid detection and remediation capabilities. The mitigation approach aligns with ATT&CK technique T1059 for command and script injection, emphasizing the need for comprehensive network security controls to prevent exploitation of such critical vulnerabilities in security infrastructure devices.