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CVE-2023-38199: coreruleset (aka OWASP ModSecurity Core Rule Set) through 3.3.4 does not detect multiple Content-Type reque...

coreruleset (aka OWASP ModSecurity Core Rule Set) through 3.3.4 does not detect multiple Content-Type request headers on some platforms. This might allow attackers to bypass a WAF with a crafted payload, aka "Content-Type confusion" between the WAF and the backend application. This occurs when the web application relies on only the last Content-Type header. Other platforms may reject the additional Content-Type header or merge conflicting headers, leading to detection as a malformed header.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This issue can let some requests look harmless to the web application firewall but be interpreted differently by the backend application. The risk depends heavily on how the platform handles duplicate Content-Type headers. The public sources do not provide a CVSS score or evidence of active exploitation.

Executive priority

Prioritize review for high-value public web applications using ModSecurity CRS. This is not proven actively exploited, but WAF bypasses can weaken a key control and should be remediated during the next security maintenance window.

Technical view

OWASP ModSecurity Core Rule Set through 3.3.4 may fail to detect requests with multiple Content-Type headers on some platforms. If the backend uses only the last Content-Type header, a WAF/backend parsing mismatch can create a Content-Type confusion bypass. Other platforms may reject or merge duplicates.

Likely exposure

Most relevant to internet-facing applications protected by OWASP ModSecurity CRS through 3.3.4 where duplicate Content-Type headers reach the backend and the application trusts the last header value.

Exploitation context

The sources describe a crafted-request WAF bypass class, not confirmed exploitation. CVE data says KEV is false. Exposure depends on intermediary, WAF, server, and application header-handling behavior.

Researcher notes

The affected scope is conditional: the flaw matters when CRS behavior differs from backend parsing. Public evidence names CRS through 3.3.4 and the Content-Type confusion scenario, but does not provide CVSS, CWE, a named fixed release, or exploit-in-the-wild evidence.

Mitigation direction

  • Check Core Rule Set guidance and deploy fixed rules when available.
  • Reject requests with duplicate Content-Type headers at the earliest controlled layer.
  • Align WAF, proxy, server, and application handling of repeated headers.
  • Review applications that choose the last Content-Type header value.
  • Monitor for malformed or repeated Content-Type headers in request logs.

Validation and detection

  • Inventory OWASP ModSecurity CRS deployments and identify versions through 3.3.4.
  • Confirm whether duplicate Content-Type headers are rejected, merged, or forwarded.
  • Verify backend applications do not trust a later conflicting Content-Type value.
  • Check WAF logs for repeated Content-Type headers and related anomaly handling.
  • Confirm vendor guidance or the referenced pull request is reflected in deployed rules.
Prepared
Confidence
medium
Sources
4

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
3Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

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