CVE-2026-103392 in Session Smart Router
Summary
by MITRE • 10/28/2026
An Out-of-Bounds Write vulnerability in the TCP header processing in Juniper Networks Session Smart Router allows an attacker to corrupt TCP payload data and potentially cause session desynchronization via a transit TCP packet with an oversized SACK option length.
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Analysis
by VulDB Data Team • 10/28/2026
The identified vulnerability resides within the Transmission Control Protocol header processing logic of the Juniper Networks Session Smart Router, specifically affecting how the device handles Selective Acknowledgment options during traffic traversal. This Out-of-Bounds Write flaw is triggered when the router processes a transit TCP packet containing an SACK option with an oversized length field that exceeds expected bounds for the allocated memory buffer. In standard network operations, routers inspect and modify headers to facilitate routing decisions or apply security policies; however, in this instance, the parsing routine fails to adequately validate the size of the SACK block before attempting to write data into a fixed-size internal structure. This lack of rigorous boundary checking allows an attacker who can inject crafted packets into the network path to cause the application to write beyond the intended memory limits associated with that specific header processing context.
The operational impact of this vulnerability is significant, primarily manifesting as potential corruption of TCP payload data and session desynchronization rather than immediate remote code execution or system crash in many scenarios. When an oversized SACK option is processed incorrectly, the resulting out-of-bounds write can overwrite adjacent memory structures that may contain critical state information for active connections. This corruption leads to a mismatch between the sender's understanding of which segments have been received and the receiver's actual buffer state, causing TCP session desynchronization. Such desynchronization typically results in severe performance degradation, connection resets, or complete denial of service for affected flows as the protocol stack attempts to recover from inconsistent state information without successful retransmission mechanisms functioning correctly due to the corrupted context.
From a classification perspective, this flaw aligns with CWE-787: Out-of-Bounds Write, which describes writing data outside the bounds of allocated memory. The attack vector leverages the normal operation of TCP SACK extensions, categorized under ATT&CK technique T1496: Resource Hijacking or potentially impacting availability through service disruption if exploited at scale to cause widespread session failures. While the primary description highlights payload corruption and desynchronization, out-of-bounds writes inherently carry risks that could escalate depending on memory layout and compiler protections, though the immediate observable effect is network-level instability rather than direct system compromise in this specific context.
Mitigation strategies must focus on both technical controls and operational procedures to address this risk within Juniper Networks Session Smart Router environments. The most effective remediation involves applying vendor-provided software patches or updates that correct the header parsing logic to enforce strict length validation for TCP options, particularly SACK fields, before any memory operations are performed. Administrators should ensure their systems are updated to versions where this boundary check is implemented correctly. In scenarios where immediate patching is not feasible, network segmentation and access control lists can be employed to restrict which sources can send traffic through the affected router interfaces, thereby limiting exposure to untrusted networks that might originate such crafted packets. Additionally, enabling deep packet inspection features if available may help identify and drop malformed TCP options before they reach the vulnerable processing module, although this adds performance overhead and should be weighed against security benefits.