ModSecurity's Insufficient Return Value Handling can Lead to XSS and Source Code Disclosure
ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. In versions 2.9.11 and below, an attacker can override the HTTP response’s Content-Type, which could lead to several issues depending on the HTTP scenario. For example, we have demonstrated the potential for XSS and arbitrary script source code disclosure in the latest version of mod_security2. This issue is fixed in version 2.9.12.
- Published
- Aug 5, 2025
- Updated
- Jun 17, 2026
- EPSS
- 0.3% · 20th percentile
- CWE
- CWE-252
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Report tools
Action score
27
Monitor
Low priority for now.
- CVSS
- 27 / 40 · 6.9 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.3%
CISA SSVC decision
- Exploitation
- proof of concept
- Automatable
- yes
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · GitHub_M
- 6.9
- NVD has not scored this yet; the score shown is the CNA’s.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Noroxi analysis
No Noroxi analysis for this record yet
We don't hand-write analysis for the hundreds of thousands of vulnerabilities in the database; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.
We use this product, ask for helpAffected systems
| Vendor | Product | CPE |
|---|---|---|
| owasp | modsecurity | cpe:2.3:a:owasp:modsecurity |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- owasp modsecurity2.0.0 and later · before 2.9.12
Versions reported by the vendor
Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.
owasp-modsecurity ModSecurity
- < 2.9.12affected
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Debian:11 | modsecurity-apache | before 2.9.3-3+deb11u5 | 2.9.3-3+deb11u5 |
| Debian:12 | modsecurity-apache | before 2.9.7-1+deb12u2 | 2.9.7-1+deb12u2 |
| Debian:13 | modsecurity-apache | before 2.9.11-1+deb13u1 | 2.9.11-1+deb13u1 |
| Debian:14 | modsecurity-apache | before 2.9.12-2 | 2.9.12-2 |
| openSUSE:Tumbleweed | apache2-mod_security2 | before 2.9.12-1.1 | 2.9.12-1.1 |
| SUSE:Linux Enterprise Module for Server Applications 15 SP6 | apache2-mod_security2 | before 2.9.4-150400.3.12.1 | 2.9.4-150400.3.12.1 |
| SUSE:Linux Enterprise Module for Server Applications 15 SP6 | apache2-mod_security2 | before 2.9.4-150400.3.12.1 | 2.9.4-150400.3.12.1 |
| SUSE:Linux Enterprise Server LTSS Extended Security 12 SP5 | apache2-mod_security2 | before 2.8.0-7.12.1 | 2.8.0-7.12.1 |
Same product
owasp: all recordsOther highest-scoring records for the same primary product.
- CVE-2026-52747ModSecurity: Multipart form-data parser silently strips embedded line breaks from form-field values, enabling request-body inspection bypass34Monitor
- CVE-2024-1019WAF bypass of the ModSecurity v3 release line34Monitor
- CVE-2026-42268ModSecurity: Unsigned integer underflow in @verifySSN / @verifyCPF / @verifySVNR operators32Monitor
- CVE-2026-30923libModSecurity3 denial of service via segfault when using t:hexDecode on single-character query strings32Monitor
- CVE-2021-42717ModSecurity 3.x through 3.0.5 mishandles excessively nested JSON objects.31Monitor
- CVE-2020-15598Trustwave ModSecurity 3.x through 3.0.4 allows denial of service via a special request.31Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| owasp-modsecurity ModSecurity | 2.9.12 · description | Vendor (CNA) |
| debian:modsecurity-apache | 2.9.7-1+deb12u2 · Debian:12 | Package registry (OSV) |
| opensuse:apache2-mod_security2 | 2.9.4-150400.3.12.1 · openSUSE:Leap 15.6 | Package registry (OSV) |
| suse:apache2-mod_security2 | 2.9.4-150400.3.12.1 · SUSE:Linux Enterprise Module for Server Applications 15 SP6 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- Integrity
- Availability
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- X
Weakness class (CWE)
CWE-252 · Unchecked Return ValueCVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
nvd-secondary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
- github.com/owasp-modsecurity/ModSecurity/commit/6d7e8eb18f2d7d368fb8e29516fcdeaeb8d349b8
- lists.debian.org/debian-lts-announce/2025/09/msg00008.html
Vendor advisories and official records. Exploit/PoC links are deliberately left out.