CVE-2026-33691
OWASP CRS: Whitespace padding in filenames bypasses file upload extension checks
Description
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.
INFO
Published Date :
April 2, 2026, 4:16 p.m.
Last Modified :
April 18, 2026, 8:16 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 3.1 | HIGH | [email protected] |
Solution
- Update OWASP CRS to version 3.3.9 or later.
- Update OWASP CRS to version 4.25.0 or later.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-33691.
| URL | Resource |
|---|---|
| https://github.com/coreruleset/coreruleset/commit/2a8c63512811c5dd74472becebb79a783e68ff02 | Patch |
| https://github.com/coreruleset/coreruleset/pull/4546 | Issue Tracking Patch |
| https://github.com/coreruleset/coreruleset/pull/4547 | Issue Tracking Patch |
| https://github.com/coreruleset/coreruleset/pull/4548 | Patch |
| https://github.com/coreruleset/coreruleset/releases/tag/v3.3.9 | Product Release Notes |
| https://github.com/coreruleset/coreruleset/releases/tag/v4.25.0 | Product Release Notes |
| https://github.com/coreruleset/coreruleset/security/advisories/GHSA-rw5f-9w43-gv2w | Mitigation Patch Vendor Advisory |
| http://seclists.org/fulldisclosure/2026/Apr/0 | Mailing List Third Party Advisory |
| http://www.openwall.com/lists/oss-security/2026/03/29/2 | Mailing List Third Party Advisory |
| http://www.openwall.com/lists/oss-security/2026/04/18/4 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-33691 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-33691
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-33691 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-33691 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by af854a3a-2127-422b-91ae-364da2661108
Apr. 18, 2026
Action Type Old Value New Value Added Reference http://www.openwall.com/lists/oss-security/2026/04/18/4 -
Initial Analysis by [email protected]
Apr. 07, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Added CPE Configuration OR *cpe:2.3:a:owasp:owasp_modsecurity_core_rule_set:*:*:*:*:*:*:*:* versions up to (excluding) 3.3.9 *cpe:2.3:a:owasp:owasp_modsecurity_core_rule_set:*:*:*:*:*:*:*:* versions from (including) 4.0.0 up to (excluding) 4.25.0 Added Reference Type GitHub, Inc.: https://github.com/coreruleset/coreruleset/commit/2a8c63512811c5dd74472becebb79a783e68ff02 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/coreruleset/coreruleset/pull/4546 Types: Issue Tracking, Patch Added Reference Type GitHub, Inc.: https://github.com/coreruleset/coreruleset/pull/4547 Types: Issue Tracking, Patch Added Reference Type GitHub, Inc.: https://github.com/coreruleset/coreruleset/pull/4548 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/coreruleset/coreruleset/releases/tag/v3.3.9 Types: Product, Release Notes Added Reference Type CVE: http://seclists.org/fulldisclosure/2026/Apr/0 Types: Mailing List, Third Party Advisory Added Reference Type CVE: http://www.openwall.com/lists/oss-security/2026/03/29/2 Types: Mailing List, Third Party Advisory Added Reference Type GitHub, Inc.: https://github.com/coreruleset/coreruleset/releases/tag/v4.25.0 Types: Product, Release Notes Added Reference Type GitHub, Inc.: https://github.com/coreruleset/coreruleset/security/advisories/GHSA-rw5f-9w43-gv2w Types: Mitigation, Patch, Vendor Advisory -
CVE Modified by af854a3a-2127-422b-91ae-364da2661108
Apr. 03, 2026
Action Type Old Value New Value Added Reference http://seclists.org/fulldisclosure/2026/Apr/0 -
New CVE Received by [email protected]
Apr. 02, 2026
Action Type Old Value New Value Added Description 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. Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N Added CWE CWE-178 Added Reference https://github.com/coreruleset/coreruleset/commit/2a8c63512811c5dd74472becebb79a783e68ff02 Added Reference https://github.com/coreruleset/coreruleset/pull/4546 Added Reference https://github.com/coreruleset/coreruleset/pull/4547 Added Reference https://github.com/coreruleset/coreruleset/pull/4548 Added Reference https://github.com/coreruleset/coreruleset/releases/tag/v3.3.9 Added Reference https://github.com/coreruleset/coreruleset/releases/tag/v4.25.0 Added Reference https://github.com/coreruleset/coreruleset/security/advisories/GHSA-rw5f-9w43-gv2w -
CVE Modified by af854a3a-2127-422b-91ae-364da2661108
Apr. 02, 2026
Action Type Old Value New Value Added Reference http://www.openwall.com/lists/oss-security/2026/03/29/2