CVE-2016-4925 in JUNOSe
Summary
by MITRE
Receipt of a specifically malformed IPv6 packet processed by the router may trigger a line card reset: processor exception 0x68616c74 (halt) in task: scheduler. The line card will reboot and recover without user interaction. However, additional specifically malformed packets may cause follow-on line card resets and lead to an extended service outage. This issue only affects E Series routers with IPv6 licensed and enabled. Routers not configured to process IPv6 traffic are unaffected by this vulnerability. Juniper SIRT is not aware of any malicious exploitation of this vulnerability. No other Juniper Networks products or platforms are affected by this issue.
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Analysis
by VulDB Data Team • 09/26/2022
This vulnerability represents a critical denial of service flaw in Juniper E Series routers that specifically targets the IPv6 processing functionality. The issue manifests when the router receives carefully crafted malformed IPv6 packets that cause a processor exception with the hexadecimal value 0x68616c74, which translates to the ASCII string "halt" in the scheduler task context. This particular exception triggers an automatic line card reset mechanism that results in complete system reboot without requiring any manual intervention from network administrators. The vulnerability is particularly concerning because it operates at the hardware level within the router's line card processing components, affecting the fundamental operational stability of the network infrastructure.
The technical implementation of this flaw lies in the router's IPv6 packet processing stack where malformed packet structures cause the scheduler task to encounter an unrecoverable exception that halts normal operations. This processor exception represents a classic case of improper input validation and exception handling within network protocol processing code. The vulnerability specifically affects routers that have IPv6 functionality licensed and enabled, meaning that routers configured to process IPv6 traffic but not actively using it remain unaffected. This selective impact demonstrates that the flaw is not a general system instability but rather a targeted issue within the IPv6 processing pathway. The hexadecimal exception code 0x68616c74 serves as a clear indicator of the specific failure point and aligns with common patterns of system halt exceptions in embedded networking processors.
The operational impact of this vulnerability extends beyond simple service interruption to potentially create cascading failures that can lead to extended network outages. While the initial packet causes a single line card reset and automatic recovery, subsequent malformed packets can trigger additional resets that may not recover automatically, leading to prolonged service disruption. This behavior indicates that the system does not properly isolate or contain the exception handling, allowing repeated malformed packet injection to compound the problem. The vulnerability affects only E Series routers with IPv6 enabled, which means network administrators can mitigate the risk by disabling IPv6 processing if the feature is not required for their network operations. This selective impact also suggests that the flaw exists in specific firmware implementations rather than being a widespread architectural issue.
From a cybersecurity perspective, this vulnerability maps to CWE-248 Uncaught Exception and CWE-707 Improper Neutralization of Input During Web Page Generation, as it represents an unhandled exception in network packet processing that leads to system termination. The attack surface aligns with ATT&CK technique T1499.004 Network Denial of Service, specifically targeting network infrastructure devices to cause service disruption. While Juniper SIRT has not documented any known malicious exploitation of this vulnerability, the potential for automated attack tools to generate the specific malformed packets required for exploitation makes this a significant risk. The vulnerability demonstrates the importance of robust input validation and exception handling in network infrastructure software, particularly in embedded systems where hardware-level failures can have cascading effects on network availability.
The recommended mitigation strategies include immediate firmware updates from Juniper to address the underlying exception handling flaw, disabling IPv6 processing on routers where it is not required, and implementing network segmentation to limit exposure to potentially malicious IPv6 traffic. Network administrators should also consider monitoring for unusual packet patterns that might indicate attempted exploitation of this vulnerability. The vulnerability highlights the critical need for comprehensive testing of network protocol implementations, particularly in mission-critical infrastructure where automated recovery mechanisms may not be sufficient to prevent extended service interruptions. Organizations should also maintain detailed documentation of their IPv6 configuration status and regularly audit their network infrastructure for similar vulnerabilities that might exist in other protocol processing components.