# CVE-2026-91772: Halo open redirect vulnerability in thumbnail endpoint

Source: https://junglewise.ai/threats/cve-2026-91772-halo-open-redirect-vulnerability-in-thumbnail-endpoint  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-15. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-91772 · Severity: medium · CVSS 6.1 · Published 2026-09-15

Halo is an open-source website builder and blogging platform. The application contains an open redirect flaw in its thumbnail endpoint that fails to validate user-supplied URLs, allowing attackers to craft malicious links that redirect users to arbitrary external websites. This can be exploited for phishing attacks and to abuse the trust placed in the Halo domain itself.

Technologies: [Halo](https://junglewise.ai/threats/technologies/halo). Vendors: [Halo](https://junglewise.ai/threats/vendors/halo).

## Quick answers

**Is CVE-2026-91772 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-91772 being exploited in the wild.

**How severe is CVE-2026-91772?** Medium severity, with a CVSS score of 6.1, published 15 September 2026.

**Which products and versions are affected?** Halo through 2.26.1.

**Is there a fix for CVE-2026-91772?** 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-2026-91772 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-91772?** Check whether you run Halo 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 open redirect in the anonymous thumbnail endpoint (/thumbnails/-/via-uri) that fails to properly validate the uri query parameter. Attackers can craft a specially designed URL on a trusted Halo instance that redirects visitors to attacker-controlled external sites without warning. The flaw exists because input validation is insufficient when processing user-controlled URI parameters. No authentication is required to exploit this vulnerability as the endpoint is anonymously accessible. While this enables phishing and trust abuse, no direct code execution or data breach occurs. A patch is expected to be available in a version after 2.26.1.

## Affected products

- Halo Halo through 2.26.1

## Timeline

- 2026-09-15: disclosed

## References

- [https://github.com/halo-dev/halo](https://github.com/halo-dev/halo)
- [https://github.com/halo-dev/halo/blob/v2.26.1/application/src/main/java/run/halo/app/core/endpoint/theme/ThumbnailEndpoint.java](https://github.com/halo-dev/halo/blob/v2.26.1/application/src/main/java/run/halo/app/core/endpoint/theme/ThumbnailEndpoint.java)

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