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Review reviewHigh

CVE-2026-33691

coreruleset coreruleset, owasp modsecurity core rule set

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.

CVSS
7.5
EPSS
3.58%
88.2% percentile
CISA KEV
Not listed
Published
2026.04.03
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability3.58%
Technical severityCVSS 7.5

Vulnerability overview

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.

Affected product and versions

Product
coreruleset coreruleset, owasp modsecurity core rule set
Affected versions
>= < 3.3.9, >= >= 4.0.0-rc1, < 4.25.0, < 3.3.9, >= 4.0.0 < 4.25.0
Fixed versions
3.3.9, 4.25.0

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that coreruleset coreruleset, owasp modsecurity core rule set and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CWE
CWE-178
CVE-2026-33691 — coreruleset coreruleset, owasp modsecurity core rule set | SECUFOCUS NOW