External risk intelligence

Jenkins Remoting JEP-200 Deserialization Filter Bypass

CVE advisorySeverity: CRITICAL (CVSS 9.0)

CVE-2026-70426

The vulnerability affects Jenkins Remoting, specifically involving communication between Jenkins controllers and agents. While these components use network connections, they are typically deployed within internal, segmented infrastructure rather than directly exposed to the public internet.

Deserialization

Halo Surface Signal: 2 out of 5 — less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A security vulnerability has been identified in Jenkins Remoting, a component used for communication between Jenkins controllers and agents. This issue could allow unauthorized parties to bypass security filters, potentially leading to the execution of malicious code. The main concern is to confirm if our environment uses the affected components and is exposed.

Bypasses security filters during code processing.
Affects Jenkins controller-agent communication.
Confirm relevance and exposure of Jenkins Remoting.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by initiating a connection to a Jenkins agent, or by leveraging existing agent processes. This bypasses security filters during deserialization, allowing for the potential execution of arbitrary code.

Requires network access to Jenkins agent.
Bypasses deserialization filter.
Risk of arbitrary code execution.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an attacker to bypass deserialization filters when agent processes resolve classes, potentially affecting code running on agents or attackers with specific permissions. This bypass could occur when classes are resolved through a fallback path in the Remoting deserialization implementation.

Agent processes and code.
Bypassing deserialization filters.
Unauthorized code execution on agents.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in Jenkins Remoting affects the deserialization process when using a fallback path, potentially allowing unauthorized code execution by agents or attackers with specific permissions. The first practical step is to identify all Jenkins controllers and agents, confirm their exposure and criticality, and then engage the Jenkins administrators or platform team responsible for remediation.

Owner: Jenkins administrators and platform teams.
Verify: Agent reachability and exposed Jenkins instances.
Action: Plan coordinated updates during maintenance.

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.

Free EASM Trial See How Signal Works

Frequently asked questions

What is Jenkins Remoting and how is it used?

Jenkins Remoting is a communication layer that links Jenkins controllers to agents. It enables distributed builds by allowing the controller to send tasks to agents—separate computing environments—for execution. This library manages the underlying network connections and data serialization between these distributed system components.

What does CVE-2026-70426 mean by a deserialization filter bypass?

This vulnerability involves CWE-502, or Deserialization of Untrusted Data. Normally, Jenkins uses a JEP-200 filter to restrict which Java classes can be processed during communication. This flaw allows data to use a fallback path that ignores these security restrictions, potentially permitting unauthorized code to run when the system processes incoming objects.

How can an attacker trigger this vulnerability?

An attacker needs the ability to communicate with the Jenkins agent or must already control an agent process with specific permissions. Importantly, the vulnerability does not trigger during standard, authorized communication that follows the primary, secured filter path; it specifically relies on triggering the insecure fallback mechanism during class resolution.

Is my Jenkins instance at risk?

According to Halo Surface Signal, this vulnerability is classified as unlikely for many because Jenkins agent communication is typically restricted to internal, segmented networks. You should prioritize assessing instances where agents are reachable from untrusted network segments, as public internet exposure significantly increases the potential risk profile.

What is the first step to address this issue?

Start by auditing your infrastructure to create an inventory of all Jenkins controllers and agents. Once identified, coordinate with your platform teams or Jenkins administrators to check if your installed versions fall within the affected range. Planning for an update to a secure version is the standard path to remediation.

References

www.jenkins.io/security/advisory/2026-08-05/

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.