# CVE-2026-33691 — coreruleset

> As of 2026-04-18, CVE-2026-33691 is a MEDIUM-severity vulnerability in coreruleset, CVSS v3.1 6.8, EPSS 1.5% (74.7th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-33691, most recently “CVE-2026-8037: Pre-Auth Command Injection RCE in Progress Kemp LoadMaster via Uninitialized-Heap escape_quotes() Flaw on /accessv2”.

**Last updated:** 2026-04-18

## What is CVE-2026-33691?

The OWASP core rule set (CRS) is a set of generic attack detection rules for use with compatible web application firewalls. Prior to versions 3.3.9 and 4.25.0, a bypass was identified in OWASP CRS that allows uploading files with dangerous extensions (.php, .phar, .jsp, .jspx) by inserting whitespace padding in the filename (e.g. photo. php or shell.jsp ). The affected rules do not normalize whitespace before evaluating the file extension regex, so the dot-extension check fails to match. This issue has been patched in versions 3.3.9 and 4.25.0.

The record classifies CVE-2026-33691 under weakness class [CWE-178](https://cwe.mitre.org/data/definitions/178.html). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on integrity. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 191 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 6.8 — MEDIUM (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N`)
- **EPSS (FIRST):** 1.5% probability of exploitation in the next 30 days, higher than 74.7% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 6.4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-04-02, last modified 2026-04-18

## Is CVE-2026-33691 being exploited?

It currently carries a trending score of 24 in the Threadlinqs vulnerability feed.

## Affected products and versions

- **coreruleset**: coreruleset

## How to fix CVE-2026-33691

No vendor patch reference has been recorded for CVE-2026-33691 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-33691

1 tracked threat in the Threadlinqs corpus references CVE-2026-33691, either in the campaign’s CVE list or as an indicator on the campaign record.

- [CVE-2026-8037: Pre-Auth Command Injection RCE in Progress Kemp LoadMaster via Uninitialized-Heap escape_quotes() Flaw on /accessv2](https://intel.threadlinqs.com/threat/TL-2026-1045) — CRITICAL · 2026-07-01

## Sources

Enriched from CVE.org, FIRST EPSS. Last verified by Threadlinqs on 2026-10-10.

**Vendor advisory and patch**

- [github.com](https://github.com/coreruleset/coreruleset/security/advisories/GHSA-rw5f-9w43-gv2w)

**Other references**

- [github.com](https://github.com/coreruleset/coreruleset/pull/4546)
- [github.com (4547)](https://github.com/coreruleset/coreruleset/pull/4547)
- [github.com (4548)](https://github.com/coreruleset/coreruleset/pull/4548)
- [github.com (2a8c63512811c5dd74472becebb79a783e68ff02)](https://github.com/coreruleset/coreruleset/commit/2a8c63512811c5dd74472becebb79a783e68ff02)
- [github.com (v3.3)](https://github.com/coreruleset/coreruleset/releases/tag/v3.3.9)

_Showing 6 of 7 recorded references._

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-33691
Full detection coverage and IOCs for threats exploiting CVE-2026-33691 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp