# CVE-2026-84655: Jenkins REST API JSON key injection

Source: https://junglewise.ai/threats/cve-2026-84655-jenkins-rest-api-json-key-injection  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-02. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-84655 · Severity: medium · CVSS 4.3 · Published 2026-09-02

Jenkins, a widely-used continuous integration and delivery server, has a flaw in how it serializes data to JSON and Python formats via its REST API. Attackers who can control map property names can inject arbitrary fields into API responses, potentially leading to information disclosure or manipulation of Jenkins configuration and operational data.

Technologies: [Jenkins](https://junglewise.ai/threats/technologies/jenkins). Vendors: [Jenkins](https://junglewise.ai/threats/vendors/jenkins).

## Quick answers

**Is CVE-2026-84655 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-84655 being exploited in the wild.

**How severe is CVE-2026-84655?** Medium severity, with a CVSS score of 4.3, published 2 September 2026.

**Which products and versions are affected?** Jenkins 2.579 and earlier, LTS 2.568.2 and earlier.

**Is there a fix for CVE-2026-84655?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-84655 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-84655?** Check whether you run Jenkins at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is an improper output encoding flaw in Jenkins' REST API JSON and Python serialization logic. When serializing objects with map-type properties, Jenkins fails to escape map keys before inserting them into JSON and Python API responses. An attacker able to control map property names (typically through configuration or object submission) can inject arbitrary fields into these responses. This requires network access to the REST API and the ability to control object properties—often possible for users with permissions to modify configurations. The impact includes information disclosure through field injection and potential manipulation of API consumer behavior if downstream systems trust the injected fields. Fix: upgrade to Jenkins 2.580 or LTS 2.568.3 or later.

## Affected products

- Jenkins Jenkins 2.579 and earlier, LTS 2.568.2 and earlier

## Timeline

- 2026-09-02: disclosed
- 2026-09-02: advisory: Jenkins Security Advisory 2026-09-02

## References

- [https://www.jenkins.io/security/advisory/2026-09-02/](https://www.jenkins.io/security/advisory/2026-09-02/)

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