Description

An Integer Underflow vulnerability in the kernel of Juniper Networks Junos OS with Extended Echo configured allows an unauthenticated, network-based attacker to cause a denial of service by a kernel crash.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.8",
  "pubDate": "2026-10-14T17:17:50.503Z",
  "pubdate": "2026-10-14T17:17:50.503Z",
  "executiveSummary": "This vulnerability involves an integer underflow flaw within the kernel of Juniper Networks Junos OS, specifically triggered when Extended Echo is enabled.\nThe vulnerability allows an unauthenticated, remote attacker to trigger a system-wide denial of service by inducing a kernel panic.\nThe flaw resides in the processing logic for Extended Echo packets, where improper handling of arithmetic operations leads to an integer underflow condition.\nSuccessful exploitation results in an immediate crash of the kernel, rendering the affected device unresponsive and disrupting all network services processed by the device.\nBecause the vulnerability is exploitable via network-based traffic without requiring authentication or specific user privileges, it presents a significant risk to the availability of Junos OS-based infrastructure.\nOrganizations utilizing Junos OS with Extended Echo enabled are at risk of remote service disruption and should prioritize the application of vendor-provided patches or the implementation of restrictive traffic controls to mitigate unauthorized exploitation.",
  "technicalDetails": "The vulnerability is rooted in an integer underflow condition occurring within the kernel-space processing logic of Junos OS, specifically affecting the component responsible for managing Extended Echo traffic.\nAn integer underflow occurs when a subtraction operation results in a value smaller than the minimum representable integer for the data type, often causing the value to wrap around to a very large positive number due to two's complement representation.\nIn this specific context, the kernel likely performs arithmetic on length or offset fields extracted directly from the Extended Echo packet headers. If these fields are improperly validated or constrained, an attacker can craft a malicious packet where the calculated length or index value underflows.\nThe attack flow proceeds as follows: 1) The attacker transmits a specially crafted network packet intended for the Extended Echo service on a target Junos OS device. 2) The kernel's packet processing routine parses the Extended Echo headers. 3) An arithmetic operation, such as subtracting a header-defined offset from a pointer or length variable, triggers the underflow because the header values are manipulated to be intentionally small or zero. 4) The resulting underflowed value is subsequently used in memory access operations, such as buffer allocation, memory copying (memcpy), or pointer arithmetic within kernel memory.\nBecause the underflow leads to an invalid, excessively large, or out-of-bounds memory address/size calculation, the kernel's memory protection mechanisms or logic checks are breached. This triggers an exception—typically a kernel panic or an unrecoverable memory fault—leading to an immediate denial of service.\nThe vulnerability is exploitable remotely over the network, as the Extended Echo implementation processes incoming traffic at the kernel level without requiring the attacker to have established a session or possess authentication credentials. No elevated privileges are required to send the malicious packet, as the attack vector relies purely on the target's exposed network interface.\nThe primary post-exploitation impact is a system crash. There is currently no evidence suggesting that this specific integer underflow is exploitable for arbitrary code execution, though it effectively facilitates a complete denial of service for the network appliance.\nThe vulnerability manifests within the kernel context, meaning the impact is not limited to a single user-space process but affects the entire operating environment, necessitating a hard reboot of the system to restore normal operations."
}