Advisories for Npm/Stream-Json package

FlexAssembler, the custom-container assembler shipped in the stream-json package (src/core/utils/flex-assembler.js, re-exported at stream-json/utils/flex-assembler.js and stream-json/web/utils/flex-assembler.js), compiles a string or RegExp path filter into a matcher that runs keyStack.join(separator) on every container start. Because the key stack grows one entry per open object or array with no depth bound, a JSON document nested to depth D drives D container-start tokens that each perform an O(D) join, for O(D^2) total CPU on …

The JSONC parser (stream-json/jsonc/parser.js) and verifier (stream-json/jsonc/verifier.js) scan a comment for its terminator starting from the comment's opening / on every input chunk. When a comment doesn't finish inside the current buffer, the scanner returns the comment's start offset and the buffer keeps the whole comment, so the next chunk re-scans everything seen so far. A single comment of length n delivered across many chunks costs O(n²) CPU. This is …

A prototype-pollution vulnerability in stream-json lets attacker-controlled JSON replace a parsed object's prototype.

The path filters pick, ignore, filter, and replace — the library's headline "surgical extraction" feature — recompute the full path string from the nesting stack on every checkable token. Because the stack length equals the current nesting depth, and a checkable token is emitted at every level, processing a document of depth D costs O(D²), not O(D). This is triggered by document structure (nesting depth), not byte volume, so a …