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fix: decode WHATWG-escaped characters in file originalname - #1421
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UlisesGascon merged 2 commits intoAug 25, 2026
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Browsers escape the bytes 0x0A (LF), 0x0D (CR) and 0x22 (") as %0A, %0D
and %22 when serialising filenames in a multipart/form-data body, per the
WHATWG HTML spec. Busboy leaves them escaped, so a file named `file".ext`
was exposed as `file%22.ext` on `req.file.originalname`.
Reverse exactly those three sequences when building the file object. Only
these are decoded on purpose: a bare `%` is never escaped by the spec, so
a full decodeURIComponent would corrupt legitimate names like `50%.pdf`.
Adds regression tests covering the escaped quote, CR/LF, an unescaped
name, and preservation of a literal percent sign.
Fixes expressjs#836
UlisesGascon
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config/morgan.js: colors moved out of the token and into the format string, where morgan doesn't touch them Dependency Release Notes: Multer v2.3.0 - Fix [CVE-2026-77078](https://www.cve.org/CVERecord?id=CVE-2026-77078) ([GHSA-wc9g-mqfw-jrwm](GHSA-wc9g-mqfw-jrwm)) - Fix [CVE-2026-77037](https://www.cve.org/CVERecord?id=CVE-2026-77037) ([GHSA-qfvm-cv95-jqjf](GHSA-qfvm-cv95-jqjf)) - Fix [CVE-2026-77063](https://www.cve.org/CVERecord?id=CVE-2026-77063) ([GHSA-qvfw-j98x-7q72](GHSA-qvfw-j98x-7q72)) - Fix [CVE-2026-82333](https://www.cve.org/CVERecord?id=CVE-2026-82333) ([GHSA-535w-7cp7-47q4](GHSA-535w-7cp7-47q4)) - Add `MulterError` codes `INVALID_FIELD_NAME` and `STREAM_DESTROYED` - Add opt-in `limits.fieldArrayIndexLimit` to bound numeric array indexes in field names ([#1438](expressjs/multer#1438)) - Accept files whose size is exactly `limits.fileSize` ([#1407](expressjs/multer#1407)) - Preserve the caller's async context (`AsyncLocalStorage`) when calling `next()` ([#1124](expressjs/multer#1124)) - Decode WHATWG-escaped characters (`%0A`, `%0D`, `%22`) in `file.originalname` ([#1421](expressjs/multer#1421)) - Do not crash when `fileFilter` invokes its callback more than once ([#1427](expressjs/multer#1427)) - Use a fallback message for `MulterError` codes without a mapping ([#1448](expressjs/multer#1448)) - Docs: clarify `preservePath` and `parts`, use `crypto.randomBytes` in the `DiskStorage` example ([#1414](expressjs/multer#1414), [#1430](expressjs/multer#1430), [#1436](expressjs/multer#1436)) - Docs: add Indonesian, Japanese and Tamil translations and refresh all translations from the current README ([#1431](expressjs/multer#1431), [#1354](expressjs/multer#1354), [#1462](expressjs/multer#1462)) - Internal: run the test suite on Windows ([#1334](expressjs/multer#1334)) Morgan 1.12.0 - Security fix for [CVE-2026-15603](https://www.cve.org/CVERecord?id=CVE-2026-15603)([GHSA-jxfw-x594-9x9m](https://github.com/expressjs/morgan/security/advisories/GHSA-jxfw-x594-9x9m)) - Allow format functions to return objects for streams in `objectMode` - Respect the `NO_COLOR` environment variable in the `dev` format
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What & why
Fixes #836.
Browsers escape the bytes
0x0A(LF),0x0D(CR) and0x22(") as%0A,%0Dand%22when serialising a filename in amultipart/form-databody, per the WHATWG HTML spec. Busboy leavesthem escaped, so a file uploaded as
file".extwas exposed onreq.file.originalnameasfile%22.ext.Change
lib/make-middleware.js.%is never escapedby the spec, so a full
decodeURIComponentwould corrupt legitimate nameslike
50%off.pdf. A dedicated test guards this.Reproduction (before)
Uploading a file named
file".ext→req.file.originalname === 'file%22.ext' // ❌ before
req.file.originalname === 'file".ext' // ✅ after
Tests
Adds
test/filename-decoding.jscovering:%22)%0D,%0A)50%off.ext)All pass;
standardlint is clean. Targeting the 2.x line as discussed onthe issue.