probe-image-size gets image dimensions without downloading the entire file. Prior to 7.4.0, lib/parse_sync/svg.js and lib/parse_stream/svg.js use the searching regular expression /<[-_.:a-zA-Z0-9][^>]*>/, which repeatedly scans to the end of input when attacker-controlled data contains many less-than characters without a closing greater-than character. The synchronous parser converts and scans the full supplied buffer without an input cap, while the streaming parser reparses the complete accumulated SVG prefix for every received chunk. The probe.sync(), probe(stream), and probe(url) entry points can therefore block the Node.js event loop at full CPU, and attacker-controlled chunking can amplify the streaming cost. This issue is fixed in version 7.4.0.

Affected: npm: probe-image-size

## Overview

`probe-image-size` scans the SVG header with a searching regular expression, `/<[-_.:a-zA-Z0-9][^>]*>/`. On input that contains many `<` characters but no `>`, the engine restarts the `[^>]*` scan at every `<` position and runs to end of input each time, giving quadratic time complexity.

Both the synchronous and the streaming parser are affected.

## Impact

Every entry point that reaches the SVG parser is affected: `probe.sync()`, `probe(stream)` and `probe(url)`. The URL form is the most exposed one — the input is fetched from a remote host, so an attacker only needs to supply a link.

Processing a crafted buffer blocks the Node.js event loop at 100% CPU for the whole duration. In production environments such as upload validators, image proxies or link unfurl services, a small number of concurrent requests is enough to deny service.

## Root Cause Analysis

Two independent problems.

1. **Absence of input size cap in the sync path.** `lib/parse_sync/svg.js` copied the entire buffer into a string and matched against it. There was no size limit at all, so cost scaled with the size of the attacker-supplied buffer.

2. **Repeated rescanning in the stream path.** `lib/parse_stream/svg.js` did cap accumulated data at 64 KB, but called `parseSvg(str)` on the whole accumulated string on *every* chunk, giving `O(chunks × N²)`. The cap does not help here: the more chunks the input is split into, the more times the quadratic scan is repeated.

Chunk size is influence…