# CVE-2026-103866: Apache Sling Engine HTTP request smuggling

Source: https://junglewise.ai/threats/cve-2026-103866-inconsistent-interpretation-of-http-requests-http-request  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-05. Updated: 2026-11-05  
License: CC BY 4.0 with a link back

CVE-2026-103866 · Severity: info · Published 2026-11-05

Apache Sling Engine is a web request processing component used in content management and web application frameworks. A flaw in how it parses HTTP requests allows attackers to send malformed requests that bypass security filters or cache poisoning by exploiting inconsistent interpretation of percent-encoded characters and invalid charsets. An attacker could use this to smuggle requests that perform unauthorized actions or access restricted content.

Technologies: [Apache Sling Engine](https://junglewise.ai/threats/technologies/sling-engine). Vendors: [Apache](https://junglewise.ai/threats/vendors/apache).

## Quick answers

**Is CVE-2026-103866 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-103866 being exploited in the wild.

**How severe is CVE-2026-103866?** Informational severity, published 5 November 2026.

**Which products and versions are affected?** Apache Sling Engine before 3.0.4.

**Is there a fix for CVE-2026-103866?** Yes: fixed in 3.0.4. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-103866 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-103866?** Check whether you run Apache Sling Engine 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.

## How to fix

- Fixed in 3.0.4

## Technical details

The query and form parser in Apache Sling Engine accepts non-standard percent-escape sequences and incorrect character encodings, then continues processing requests despite these errors. This inconsistent interpretation of HTTP requests enables request smuggling attacks, where an attacker crafts malformed input to manipulate how the engine and downstream components (firewalls, proxies, caches) parse the request, leading to security bypass. The vulnerability requires network access and no authentication.

## Affected products

- Apache Sling Engine before 3.0.4

## References

- [https://lists.apache.org/thread.html/yoftbty2lc7kmtldmyvj7w0m0n1ncbf6](https://lists.apache.org/thread.html/yoftbty2lc7kmtldmyvj7w0m0n1ncbf6)

## Related threats

- [Apache Sling Engine improper output neutralization in logs](https://junglewise.ai/threats/cve-2026-103864-improper-output-neutralization-for-logs-in-apache-sling-engine)
- [Apache Sling Engine cross-site scripting in header handling](https://junglewise.ai/threats/cve-2026-103863-improper-neutralization-of-input-during-web-page-generation)