Memory-exhaustion DoS in BMP decoder (bundled bmp-ts dependency) via unbounded width/height

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Summary

@jimp/js-bmp delegates BMP decoding entirely to the bmp-ts npm package with no validation of its own. bmp-ts's decoder allocates its output pixel buffer directly from the BMP header's width/height fields with no upper bound and no comparison against the actual input size:

// bmp-ts@1.0.9 dist/commonjs/decoder.js:153
this.data = Buffer.alloc(this.width * this.height * 4);

For RLE4/RLE8-compressed BMPs, the very next thing that happens is:

// decoder.js:201 (bit4) and :279 (bit8)
this.data.fill(0);

Buffer.fill() forces real physical memory to be committed across the whole buffer (unlike Buffer.alloc's lazily-zero-mapped pages), and this happens before any actual pixel bytes are read from the file, so a tiny file with a big declared width/height is enough to force a large real memory allocation.

Proof of Concept

A crafted 1078-byte BMP (valid BM magic + 40-byte BITMAPINFOHEADER, bitPP=8, compression=1 i.e. BI_RLE8, width=10000, height=10000, a 256-entry zero palette, and no actual RLE pixel data after the palette) causes roughly 405MB of RSS growth in a single Jimp.read() call, confirmed against the real published jimp@1.6.1 (which bundles bmp-ts@1.0.9):

input size 1078 bytes   rss before ~67.7MB
Jimp.read(buffer) -> eventually throws RangeError (only AFTER the .fill(0) commits memory)
time 278ms              rss after ~472.4MB   (~405MB forced commit from a 1KB file)

Scaling width/height further is unbounded — nothing in bmp-ts or in @jimp/js-bmp's wrapper (plugins/js-bmp/src/index.ts, which calls BMP.decode() directly with no width/height sanity check before delegating) caps the allocation. A handful of concurrent uploads of ~1KB crafted files could force multi-GB memory growth or an allocator OOM in any service that calls Jimp.read() on user-uploaded images (a very common pattern — avatar/image upload handling).

This is a memory-exhaustion availability issue (CWE-400/789), not memory corruption — Node's Buffer/TypedArray bounds checks prevent any actual out-of-bounds read/write.

Suggested Fix

Before allocating the output buffer, validate that width * height * bytesPerPixel is consistent with the actual input buffer size (or with a reasonable configurable maximum), and reject the file early if not. This applies both in bmp-ts's decoder.js (root cause) and as a defense-in-depth check in @jimp/js-bmp's wrapper before it delegates to bmp-ts, since jimp is the package most people actually depend on directly.

Disclosure note

Checked for existing reports first: no GHSA/CVE/OSV advisory exists for bmp-ts, jimp, or @jimp/js-bmp. Neither repo has SECURITY.md or GitHub private vulnerability reporting enabled, so filing this as a plain public issue rather than a private advisory — severity is DoS-only (not RCE/memory-corruption), so this seemed reasonable to disclose directly; happy to move to a private channel if one gets set up.