Provisional finding. Full causal and release verification remains incomplete.
Go's MIME parser ignores filename* in charsets other than UTF-8 and ASCII, so FILES rules saw a decoy name; code before 3.8.0 trusted it. The 3.8.0 remediation added RFC 2231 continuation checks in Claude-co-authored commits but skipped them when a plain filename* was also present, which some backends resolve. 3.8.1 flags it.
AI-assisted change
The original trust in Go's MIME-parsed filename predates this AI change; the Claude Sonnet 5 co-authored 3.8.0 remediation records filename* metadata and alternate names but skips continuation checks when a bare filename* is present.
Root cause
A multipart sender can put a decoy plain filename and a filename* beside an RFC 2231 continuation; Werkzeug may resolve the continuation while Coraza exposes only the decoys and raises no strict error.
Fix
The 3.8.1 repair marks that continuation as malformed, so the strict-error signal and rule 200003 can reject the ambiguous multipart part.
Case facts
ClaudeCite this finding
Vibe Security Radar, "GHSA-3WR7-993Q-JRFF in corazawaf/coraza," Georgia Tech SSLab, https://vibesecradar.com/cves/GHSA-3WR7-993Q-JRFF/
@@ -39,6 +39,10 @@ func (mbp *multipartBodyProcessor) ProcessRequest(reader io.Reader, v plugintype filesCombinedSizeCol := v.FilesCombinedSize() filesNamesCol := v.FilesNames() headersNames := v.MultipartPartHeaders()+ multipartFilenameCol := v.MultipartFilename()+ multipartFilenameCharsetCol := v.MultipartFilenameCharset()+ multipartFilenameLanguageCol := v.MultipartFilenameLanguage()+ multipartNameCol := v.MultipartName() for { p, err := mr.NextPart() if err == io.EOF {@@ -49,13 +53,57 @@ func (mbp *multipartBodyProcessor) ProcessRequest(reader io.Reader, v plugintype return err } partName := p.FormName()+ duplicateHeader := false for key, values := range p.Header {+ if len(values) > 1 {+ duplicateHeader = true+ } for _, value := range values { headersNames.Add(partName, fmt.Sprintf("%s: %s", key, value)) } }+ fields := originFileName(p)+ if duplicateHeader || fields.duplicateParam {+ v.MultipartDuplicatePartHeader().(*collections.Single).Set("1")+ }+ if fields.invalidQuoting {+ v.MultipartInvalidQuoting().(*collections.Single).Set("1")+ }+ if duplicateHeader || fields.duplicateParam || fields.malformed || fields.invalidQuoting {+ v.MultipartStrictError().(*collections.Single).Set("1")+ }+ // Add, not Set: distinct parts sharing one "name" (e.g. a multi-file+ // input) must each keep their own filename visible to rules. Set+ // would let the last part silently overwrite the ones before it,+ // the same class of bypass this advisory already covers -- see+ // ModSecurity's GHSA-5pww-8rfg-9crf, which names this "a second,+ // distinct bypass" fixed by keeping MULTIPART_FILENAME/_NAME as+ // multi-valued collections rather than single overwritable slots.+ multipartNameCol.Add(partName, partName)+ if fields.filename != "" {+ multipartFilenameCol.Add(partName, fields.filename)+ }+ // altFilename is the reading a backend using different filename*+ // precedence than Coraza would resolve instead: added alongside the+ // primary one rather than picking a side, so a rule matches whichever+ // name is actually used downstream.+ if fields.altFilename != "" {+ multipartFilenameCol.Add(partName, fields.altFilename)+ }+ if fields.hasExtended {+ multipartFilenameCharsetCol.Add(partName, fields.charset)+ multipartFilenameLanguageCol.Add(partName, fields.language)+ } // if is a file- filename := originFileName(p)+ filename := fields.filename+ if filename == "" {+ // An extended "filename*" that decodes to the empty string (e.g.+ // filename*=utf-8'') would otherwise misclassify the part as a+ // field even though a non-empty plain "filename" is present --+ // PHP, Go mime/multipart, python-multipart and formidable all+ // still resolve it as a file. See GHSA-3wr7-993q-jrff review.+ filename = fields.altFilename+ } if filename != "" { var size int64 seenUnexpectedEOF := false@@ -98,6 +146,15 @@ func (mbp *multipartBodyProcessor) ProcessRequest(reader io.Reader, v plugintype totalSize += size filesCol.Add("", filename) fileSizesCol.SetIndex(filename, 0, fmt.Sprintf("%d", size))+ if fields.altFilename != "" && fields.altFilename != filename {+ // Same part, same bytes, same size -- just a second name a+ // differently-implemented backend might resolve instead.+ // (Skipped when equal to filename: that happens when+ // fields.filename was empty and altFilename was already+ // promoted to primary above -- not two distinct readings.)+ filesCol.Add("", fields.altFilename)+ fileSizesCol.SetIndex(fields.altFilename, 0, fmt.Sprintf("%d", size))+ } filesNamesCol.Add("", p.FormName()) filesCombinedSizeCol.(*collections.Single).Set(fmt.Sprintf("%d", totalSize)) if seenUnexpectedEOF {@@ -132,19 +189,333 @@ var ( _ plugintypes.BodyProcessor = (*multipartBodyProcessor)(nil) ) @@ -335,6 +335,13 @@ func originFileName(p *multipart.Part) filenameFields { } return f }+ // A continuation alongside a bare "filename*" is not reassembled either,+ // and Werkzeug/Flask lets the continuation win over both "filename*" and+ // "filename", so the value a backend resolves may be one Coraza never+ // exposes. Flag it the same way as the continuation-only case above.+ if hasFilenameContinuation(cd) {+ f.malformed = true+ } // RFC 5987 does not permit ext-value to be a quoted-string, but a // general Content-Disposition parameter parser -- Go's mime.ParseMediaType // included -- accepts a quoted-string for any parameter, filename*AI-assisted change 54f1b6fea6d8b94ceb53ab4aa9adde84892f88c61f7075168384c8516311bd8f · Fix c94c8f54686bbff4dfa70b48c22c5b97b1ba4c73702107eaec0a8e4cc6fe0716
GHSA-W253-M66G-RX24Oct 8, 2026corazawaf/coraza
GoClaudeFlawed AI-written codeOther or unclear
GHSA-G4QM-M288-5CP9Oct 8, 2026corazawaf/corazaGoClaudeFlawed AI-written codeOther or unclear
CVE-2026-107826Oct 8, 2026corazawaf/corazaGoClaudeFlawed AI-written codeResource abuse & availability
GHSA-5GJ4-9GM7-2FX2Oct 8, 2026corazawaf/corazaGoClaudeFlawed AI-written codeOther or unclear
CVE-2026-41510Oct 6, 2026corazawaf/corazaGoClaudeFlawed AI-written codeInjection & unsafe execution