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CVE-2026-33691

OWASP CRS: Whitespace padding in filenames bypasses file upload extension checks

6.8 MediumFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
High
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
High
Availability
None

Exploit likelihood

3.84%Up 3.8 points since Apr 3, 2026
90%50%10%1%

What each source reports

CVE List Score used 6.8

OWASP CRS: Whitespace padding in filenames bypasses file upload extension checks

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.

Record
CVE-2026-33691
CVSS 3.1
6.8 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N
Weakness
CWE-178
Updated
2026-11-02
EUVDEUVD-2026-18352 6.8

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.

Record
EUVD-2026-18352
CVSS 3.1
6.8 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N
Updated
2026-11-02
NVD 6.8

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.

Record
CVE-2026-33691
CVSS 3.1
6.8 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness
CWE-178
Updated
2026-11-02
OSV 6.8

OWASP CRS: Whitespace padding in filenames bypasses file upload extension checks

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.

Record
CVE-2026-33691
CVSS 3.1
6.8 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N
Weakness
CWE-178
Updated
2026-11-02
OSVDEBIAN-CVE-2026-33691 7.5

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.

Record
DEBIAN-CVE-2026-33691
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated
2026-11-02
OSVUBUNTU-CVE-2026-33691 6.8

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.

Record
UBUNTU-CVE-2026-33691
CVSS 3.1
6.8 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated
2026-11-02
OSVopenSUSE-SU-2026:11632-1 No score

owasp-modsecurity-crs-4.29.0-1.1 on GA media

These are all security issues fixed in the owasp-modsecurity-crs-4.29.0-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:11632-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
modsecurity-crs
Debian:12
before 3.3.4-1+deb12u3, plus listed versions
3.3.4-13.3.4-1+deb12u13.3.4-1+deb12u2
3.3.4-1+deb12u3
modsecurity-crs
Debian:13
before 3.3.7-1+deb13u2, plus listed versions
3.3.7-13.3.7-1+deb13u1
3.3.7-1+deb13u2
modsecurity-crs
Debian:14
before 3.3.9-1, plus listed versions
3.3.7-13.3.8-1
3.3.9-1
modsecurity-crs
Ubuntu:16.04:LTS
All versions, plus listed versions
2.2.9-1
None known
modsecurity-crs
Ubuntu:18.04:LTS
All versions, plus listed versions
3.0.0-33.0.2-1
None known
modsecurity-crs
Ubuntu:20.04:LTS
All versions, plus listed versions
3.1.1-13.2.0-1
None known
modsecurity-crs
Ubuntu:22.04:LTS
All versions, plus listed versions
3.3.0-13.3.2-1
None known
modsecurity-crs
Ubuntu:24.04:LTS
All versions, plus listed versions
3.3.5-13.3.5-2
None known
modsecurity-crs
Ubuntu:25.10
All versions, plus listed versions
3.3.7-1
None known
modsecurity-crs
Ubuntu:26.10
All versions, plus listed versions
3.3.8-13.3.9-1
None known
modsecurity-crs
Ubuntu:26.04:LTS
All versions, plus listed versions
3.3.7-13.3.8-1
None known
owasp-modsecurity-crs
openSUSE:Tumbleweed
before 4.29.0-1.1
4.29.0-1.1

History

History
RecordedChangedSources
first indexedCVE List, EUVD, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-33691 is a medium vulnerability (CVSS 6.8) in Coreruleset, published April 2, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 3.84%, the 90th percentile. Fixed in modsecurity-crs 3.3.4-1+deb12u3.

References

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