External risk intelligence

Cisco Products Command Execution via Java Deserialization Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2015-6420

This vulnerability exists in the Apache Commons Collections library, a ubiquitous component in Java-based enterprise applications. Because this library is commonly used in internet-facing web applications, middleware, and application servers to process serialized objects, it is frequently deployed in services that are reachable from the public internet.

Deserialization

Apache Commons Collections

3.0 to before 3.2.24.0

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability related to the Apache Commons Collections library allows remote attackers to execute arbitrary commands by sending a specially crafted serialized Java object. This impacts a wide range of Cisco products and potentially other applications that utilize this library for object serialization.

Attackers can remotely execute code.
Critical library component used across many Java applications.
Confirm if this widely used library is in your technology stack.

Attack Path

How an attacker could exploit the issue

Attackers can exploit this vulnerability by sending a specially crafted serialized Java object to an application that uses a vulnerable version of the Apache Commons Collections library. This can be done over the network without any authentication. If successful, an attacker could execute arbitrary commands on the affected system, potentially leading to a complete system compromise.

No authentication required to trigger.
Triggered by a crafted serialized Java object.
Allows arbitrary command execution.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow remote attackers to execute arbitrary commands on affected systems when processing a crafted serialized Java object. This could impact system data and service behavior.

System data and service behavior.
Via crafted serialized Java objects.
Remote command execution.

Operational Fix

Recommended remediation, mitigation, and detection steps

The widespread use of the Apache Commons Collections library in numerous Cisco products and other Java applications means that multiple teams, including application owners, infrastructure, and platform teams, may be responsible for addressing this vulnerability. The initial practical step is to identify all instances of the affected library, determine their exposure and business criticality, and then confirm the accountable owner for each deployment before planning remediation.

Identify affected technology instances.
Verify exposure and criticality.
Plan remediation based on risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is Apache Commons Collections and why is it in Cisco products?

Apache Commons Collections is a Java library that provides extended data structures and utilities, such as specialized maps and lists, which simplify common programming tasks. Many enterprise-grade Cisco systems—including networking, unified communications, and management platforms—embed this library to handle complex data processing tasks like object serialization, where data is converted into a format suitable for storage or network transmission.

What does CWE-502 mean for CVE-2015-6420?

CWE-502, or Deserialization of Untrusted Data, refers to a weakness where an application takes data from an outside source and attempts to reconstruct it as a complex object without sufficient validation. In this CVE, the application processes a malicious serialized Java object, allowing the code to perform actions unintended by the original developer, effectively resulting in the execution of arbitrary commands on the host system.

How is this vulnerability triggered?

An attacker triggers this flaw by sending a specifically crafted serialized Java object to an application that utilizes the affected version of the Apache Commons Collections library. The vulnerability is activated during the deserialization process. Importantly, simply having the library installed is not enough; the application must be actively configured to accept and deserialize incoming Java objects from untrusted network sources to be susceptible.

Is my system at risk?

Halo Surface Signal indicates this vulnerability is likely to be relevant if you run Java-based enterprise applications or middleware exposed to the public internet. Because the library is a ubiquitous component, it often resides within services reachable from the outside. If your Cisco software or custom Java applications process serialized data from network-facing interfaces, they may be susceptible to remote exploitation.

What are the first steps to address this issue?

Begin by auditing your technology stack to locate all instances of the vulnerable Apache Commons Collections library. Since this component is often bundled deep within third-party products, coordinate with application and infrastructure teams to inventory your environment. Once identified, prioritize these instances based on their business criticality and network exposure, then work with product vendors or internal owners to determine the correct update path.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.