How severe is CVE-2026-33691?

CVE-2026-33691 has a CVSS 3.x base score of 6.8, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2026-33691 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (80th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33691?

CVE-2026-33691 affects Owasp Owasp Modsecurity Core Rule Set. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33691?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-33691 have an EU (EUVD) identifier?

Yes. CVE-2026-33691 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-18352.

When was CVE-2026-33691 published?

CVE-2026-33691 was published on 2026-04-02 and last updated on 2026-06-17.

CVE-2026-33691

CVE-2026-33691 is a medium-severity vulnerability in Owasp Owasp Modsecurity Core Rule Set with a CVSS 3.x base score of 6.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-178.

Key facts

Severity: Medium (CVSS 3.x base score 6.8)
EPSS exploit prediction: 2% (80th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-18352
Weakness: CWE-178
Affected product: Owasp Owasp Modsecurity Core Rule Set
Published: 2026-04-02
Last modified: 2026-06-17

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.

Frequently asked questions

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.
How severe is CVE-2026-33691?: CVE-2026-33691 has a CVSS 3.x base score of 6.8, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2026-33691 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (80th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33691?: CVE-2026-33691 affects Owasp Owasp Modsecurity Core Rule Set. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33691?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-33691 have an EU (EUVD) identifier?: Yes. CVE-2026-33691 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-18352.
When was CVE-2026-33691 published?: CVE-2026-33691 was published on 2026-04-02 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:owasp:owasp_modsecurity_core_rule_set:*:*:*:*:*:*:*:*

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