Widely deployed WAF rule set; bypass can enable web app compromise across multiple industries.
CVE-2026-33691
CRS whitespace padding bypasses file-extension check.
Is CVE-2026-33691 being exploited?
Not confirmed. CVE-2026-33691 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 3.6% probability of exploitation in the next 30 days.
How severe is CVE-2026-33691?
CVE-2026-33691 is rated Critical with a CVSS score of 9.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-33691?
Yes. A fix has been recorded for CVE-2026-33691. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-33691 affect?
CVE-2026-33691 affects OWASP Core Rule Set 3.x before 3.3.9, OWASP Core Rule Set 4.x before 4.25.0. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-33691?
Upgrade CRS to 3.3.9 or 4.25.0+.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Bypass WAF file-extension checks; enables uploading .php/.jsp via whitespace padding, risking remote code execution on web servers.
Patch when possible
- affected< 3.3.9
- affected>= 4.0.0-rc1 and < 4.25.0
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.