# CVE-2025-51857: Halo AttachmentReconciler cross-site scripting

Source: https://junglewise.ai/threats/cve-2025-51857-halo-attachmentreconciler-cross-site-scripting  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-08-05. Updated: 2026-07-05  
License: CC BY 4.0 with a link back

CVE-2025-51857 · Severity: medium · CVSS 6.1 · Published 2025-08-05

Halo, an open-source website building and content management platform, is affected by a security vulnerability in its attachment handling system. An attacker could potentially inject malicious scripts into the platform, which would then execute in the browser of other users or administrators who view the affected content. This could lead to unauthorized actions being performed on behalf of users, session hijacking, or the defacement of the website.

## Quick answers

**Is CVE-2025-51857 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-51857 being exploited in the wild.

**How severe is CVE-2025-51857?** Medium severity, with a CVSS score of 6.1, published 5 August 2025.

**Which products and versions are affected?** halo-dev Halo v.2.20.18LTS and before.

**Is there a fix for CVE-2025-51857?** 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-2025-51857 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2025-51857?** Check whether anything you run is named in the advisory. 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

A Cross-Site Scripting (XSS) vulnerability exists in Halo v.2.20.18LTS and earlier versions within the AttachmentReconciler class. The flaw is located in the reconcile method, which fails to properly neutralize user-supplied input during the attachment reconciliation process. An unauthenticated remote attacker can exploit this by uploading a malicious file or providing crafted input that triggers the execution of arbitrary JavaScript in the context of a victim's browser session. This is a reflected or stored XSS (depending on the reconciliation flow) requiring minimal user interaction to execute.

## Affected products

- halo-dev Halo v.2.20.18LTS and before

## Timeline

- 2025-08-04: disclosed: Initial researcher gist published
- 2025-08-05: advisory: CVE published to NVD

## References

- [https://gist.github.com/this1slwl/d714514635119159607c14faebbbcf20](https://gist.github.com/this1slwl/d714514635119159607c14faebbbcf20)
- [https://github.com/halo-dev/halo](https://github.com/halo-dev/halo)