CVE-2021-31371 in Junos OS
Summary
by MITRE • 10/19/2021
Juniper Networks Junos OS uses the 128.0.0.0/2 subnet for internal communications between the RE and PFEs. It was discovered that packets utilizing these IP addresses may egress an QFX5110 switch, leaking configuration information such as heartbeats, kernel versions, etc. out to the Internet, leading to an information exposure vulnerability. This issue affects: Juniper Networks Junos OS on QFX5110 Series: All versions prior to 17.3R3-S12; 18.1 versions prior to 18.1R3-S13; 18.3 versions prior to 18.3R3-S5; 19.1 versions prior to 19.1R3-S6; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S6, 19.3R3-S3; 19.4 versions prior to 19.4R1-S4, 19.4R3-S5; 20.1 versions prior to 20.1R2-S2, 20.1R3-S1; 20.2 versions prior to 20.2R3-S2; 20.3 versions prior to 20.3R3-S1; 20.4 versions prior to 20.4R2-S1, 20.4R3; 21.1 versions prior to 21.1R1-S1, 21.1R2;
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Analysis
by VulDB Data Team • 10/23/2021
The vulnerability described in CVE-2021-31371 represents a critical information exposure flaw within Juniper Networks Junos OS operating on QFX5110 series switches. This issue stems from the improper handling of internal communication packets that utilize the 128.0.0.0/2 subnet, which is designated for internal use between Routing Engines and Packet Forwarding Engines. The vulnerability manifests when these internally routed packets inadvertently escape the switch boundary and traverse external networks, potentially exposing sensitive configuration data to unauthorized parties. This flaw directly violates fundamental network security principles by creating an unintended information disclosure channel that undermines the isolation of internal network components.
The technical implementation of this vulnerability involves the misconfiguration of packet forwarding mechanisms within the Junos OS kernel. When packets destined for internal 128.0.0.0/2 addresses are processed by the switch's routing infrastructure, they are not properly confined to the internal network segment. Instead, these packets can be forwarded through external interfaces, carrying with them metadata including heartbeat signals, kernel version information, and other operational details that should remain within the internal administrative domain. This behavior creates a persistent exposure vector that allows remote attackers to gather intelligence about the network infrastructure without requiring direct access to the internal network.
From an operational impact perspective, this vulnerability significantly increases the attack surface for malicious actors who can leverage the leaked information to conduct more sophisticated attacks against the affected switches. The exposure of kernel versions and heartbeat information provides attackers with valuable reconnaissance data that can be used to identify potential exploits or vulnerabilities specific to the exposed software versions. The information disclosure could enable attackers to perform targeted attacks against known vulnerabilities in specific Junos OS versions, potentially leading to privilege escalation, denial of service, or complete system compromise. This vulnerability particularly affects network infrastructure that serves as critical communication hubs, where such information leakage could facilitate broader network infiltration attempts.
Security mitigations for this vulnerability primarily involve applying the vendor-provided software patches and firmware updates that address the packet forwarding logic within the Junos OS implementation. Organizations should immediately upgrade their QFX5110 switches to versions that have been released to address this specific flaw, ensuring that all affected software versions listed in the vulnerability description are properly updated. Network administrators should also implement additional monitoring and logging procedures to detect any unusual packet flows that might indicate exploitation attempts, while network segmentation strategies should be reviewed to minimize the impact of potential information leakage. The vulnerability aligns with CWE-200 (Information Exposure) and can be categorized under ATT&CK technique T1082 (System Information Discovery) and T1592 (Obtain Capabilities) in threat modeling contexts.