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Fencer Intel
high 8.6

CVE-2026-104269 json

ModSecurity: RFC 2231 `filename*` Parameter Bypasses Multipart Filename Rules on RFC-Compliant Backends (Go, Python, Node, Java)

published 4d ago modified 7h ago also EUVD-2026-117555

cvss
8.6
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 47%
public exploits
0
none known

Summary

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, ModSecurity's multipart parser does not apply the RFC 2231 filename* parameter precedence used by common Go, Python, Node.js, and Java application parsers. A Content-Disposition header can provide a benign filename parameter for ModSecurity and a different encoded filename* value that the backend prefers, causing MULTIPART_FILENAME rules and the application to make security decisions on different names. Applications that use the backend-selected name for storage, extension checks, or content-type inference can therefore receive a filename that bypassed WAF inspection. PHP's native multipart parser is not affected by this discrepancy. This issue is fixed in version 3.0.17.

Patch / fix

Is CVE-2026-104269 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-104269 updated cvss 8.6

modsecurity: mod_security: ModSecurity: Security inspection bypass via multipart filename parameter discrepancy

  • Red Hat JBoss Core Services jbcs-httpd24-mod_security, jbcs-httpd24-mod_security-src-zip
    affected: workaround, no fix available
  • Red Hat Enterprise Linux 7 mod_security-mlogc, mod_security 2.9.14-1.el10 Red Hat Enterprise Linux 8 mod_security, mod_security-mlogc, mod_security 2.9.14-1.el10 Red Hat Enterprise Linux 9 mod_security, mod_security-mlogc, mod_security 2.9.14-1.el10 Red Hat Enterprise Linux 10 mod_security 2.9.14-1.el10
    under investigation

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
8h ago

Exploit prediction

0.57% chance of exploitation in the next 30 days, higher than 47% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/owasp-modsecurity/ModSecurity/security/advisories/GHSA-5pww-8rfg-9crf referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

Affected products

  • owasp-modsecurity ModSecurity

Classification

Weakness

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.