CVE-2026-73856
ModSecurity: Response Body Inspection Bypass
ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. From 3.0.0 until 3.0.17, src/transaction.cc compares a response Content-Type value against SecResponseBodyMimeType entries case-sensitively. A mixed-case response media type that is semantically equivalent to a configured lowercase type can therefore be treated as unconfigured, causing ModSecurity to skip RESPONSE_BODY inspection. An unauthenticated requester can then receive response content that a phase 4 rule would otherwise block, including sensitive error or debug data. This issue is fixed in version 3.0.17.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- High
- Integrity
- None
- Availability
- None
Exploit likelihood
What each source reports
CVE List Score used
ModSecurity: Response Body Inspection Bypass
ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. From 3.0.0 until 3.0.17, src/transaction.cc compares a response Content-Type value against SecResponseBodyMimeType entries case-sensitively. A mixed-case response media type that is semantically equivalent to a configured lowercase type can therefore be treated as unconfigured, causing ModSecurity to skip RESPONSE_BODY inspection. An unauthenticated requester can then receive response content that a phase 4 rule would otherwise block, including sensitive error or debug data. This issue is fixed in version 3.0.17.
- Record
CVE-2026-73856- CVSS 3.1
- 8.6 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N - Weakness
- CWE-178
- Updated
- 2026-11-05
EUVDEUVD-2026-117554
ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. From 3.0.0 until 3.0.17, src/transaction.cc compares a response Content-Type value against SecResponseBodyMimeType entries case-sensitively. A mixed-case response media type that is semantically equivalent to a configured lowercase type can therefore be treated as unconfigured, causing ModSecurity to skip RESPONSE_BODY inspection. An unauthenticated requester can then receive response content that a phase 4 rule would otherwise block, including sensitive error or debug data. This issue is fixed in version 3.0.17.
- Record
EUVD-2026-117554- CVSS 3.1
- 8.6 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N - Updated
- 2026-11-05
NVD
ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. From 3.0.0 until 3.0.17, src/transaction.cc compares a response Content-Type value against SecResponseBodyMimeType entries case-sensitively. A mixed-case response media type that is semantically equivalent to a configured lowercase type can therefore be treated as unconfigured, causing ModSecurity to skip RESPONSE_BODY inspection. An unauthenticated requester can then receive response content that a phase 4 rule would otherwise block, including sensitive error or debug data. This issue is fixed in version 3.0.17.
- Record
CVE-2026-73856- CVSS 3.1
- 8.6 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N - Weakness
- CWE-178
- Updated
- 2026-11-05
OSV
ModSecurity: Response Body Inspection Bypass
ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. From 3.0.0 until 3.0.17, src/transaction.cc compares a response Content-Type value against SecResponseBodyMimeType entries case-sensitively. A mixed-case response media type that is semantically equivalent to a configured lowercase type can therefore be treated as unconfigured, causing ModSecurity to skip RESPONSE_BODY inspection. An unauthenticated requester can then receive response content that a phase 4 rule would otherwise block, including sensitive error or debug data. This issue is fixed in version 3.0.17.
- Record
CVE-2026-73856- CVSS 3.1
- 8.6 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N - Weakness
- CWE-178
- Updated
- 2026-11-07
OSVDEBIAN-CVE-2026-73856
ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. From 3.0.0 until 3.0.17, src/transaction.cc compares a response Content-Type value against SecResponseBodyMimeType entries case-sensitively. A mixed-case response media type that is semantically equivalent to a configured lowercase type can therefore be treated as unconfigured, causing ModSecurity to skip RESPONSE_BODY inspection. An unauthenticated requester can then receive response content that a phase 4 rule would otherwise block, including sensitive error or debug data. This issue is fixed in version 3.0.17.
- Record
DEBIAN-CVE-2026-73856- CVSS 3.1
- 8.6 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N - Updated
- 2026-11-06
OSVUBUNTU-CVE-2026-73856
[GHSA-vmg8-j66p-vgvw: Response body inspection bypass via non-canonical Content-Type casing]
- Record
UBUNTU-CVE-2026-73856- CVSS 3.1
- 8.6 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N - Updated
- 2026-11-07
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
modsecurityDebian:12 |
All versions, plus listed versions 3.0.10-13.0.11-13.0.12-13.0.12-1.13.0.12-1.1~exp1 Show 7 moreShow less3.0.13-13.0.14-13.0.15-13.0.16-13.0.9-13.0.9-1+deb12u13.0.9-1+deb12u2 |
None known |
modsecurityDebian:13 |
All versions, plus listed versions 3.0.14-13.0.14-1+deb13u13.0.15-13.0.16-1 |
None known |
modsecurityDebian:14 |
All versions, plus listed versions 3.0.14-13.0.15-13.0.16-1 |
None known |
modsecurityUbuntu:20.04:LTS |
All versions, plus listed versions 3.0.3-13.0.4-13.0.4-1build1 |
None known |
modsecurityUbuntu:22.04:LTS |
All versions, plus listed versions 3.0.4-23.0.6-1 |
None known |
modsecurityUbuntu:24.04:LTS |
All versions, plus listed versions 3.0.10-13.0.11-13.0.12-13.0.12-1.1build13.0.12-1.1build2 |
None known |
modsecurityUbuntu:26.10 |
All versions, plus listed versions 3.0.14-1build23.0.15-13.0.16-1 |
None known |
modsecurityUbuntu:26.04:LTS |
All versions, plus listed versions 3.0.14-1build13.0.14-1build2 |
None known |
History
| Recorded | Changed | Sources |
|---|---|---|
| published | OSV | |
| aliases, references | NVD, OSV | |
| aliases | EUVD | |
| cwes, description, facts, products, references, severity, title | CVE List | |
| first indexed | OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-73856 is a high vulnerability (CVSS 8.6) in Owasp-modsecurity Modsecurity, published October 2, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.56%, the 47th percentile. No source names a fixed version.
References
github.com/owasp-modsecurity/ModSecurity/security/advisories/GHSA-vmg8-j66p-vgvw
nvd.nist.gov/vuln/detail/CVE-2026-73856
security-tracker.debian.org/tracker/CVE-2026-73856