ModSecurity: RFC 2231 `filename*` Parameter Bypasses Multipart Filename Rules on RFC-Compliant Backends (Go, Python, Node, Java)
- Exploited
- No known exploitation
- Fix
- Fixed in 3.0.17
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 3.0.17.
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 26/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
ModSecurity, a web application firewall engine for Apache, IIS, and Nginx, can be bypassed through its multipart parser when a request uses an RFC 2231 "filename*" parameter that the application backend prefers over the filename ModSecurity inspected. An attacker can reach this remotely, without logging in, and get a file through the WAF's filename rules that the application then stores or checks under a different name, which can affect storage, extension checks, or content-type decisions.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed per the CVSS vector, reachable over the network without a login · Unknown: No advisory context yet
- Reach?/20Unknown. No tracked technology or package matched
- Severity8.6/10CVSS 8.6
- No patch0/5No signal
What would change the score
- Would score about 71 if added to CISA KEV
- Would score about 66 if CISA's SSVC rates exploitation active
- Would score about 31 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 3.0.17.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- owasp-modsecurity ModSecurity
From 3.0.0 · fixed in 3.0.17
Evidence 5
- Advisory
- Repository
- Repository
- Repository
- Repository
Corrections
None so far.
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Questions about CVE-2026-104269
Is CVE-2026-104269 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-104269?
ModSecurity: from 3.0.0 before 3.0.17.Source: cve.now feed data
How do I fix CVE-2026-104269?
Upgrade to a fixed version: 3.0.17.Source: cve.now feed data