Описание
qs array-limit bypass via bracket-key comma parsing
Summary
qs v6.15.3 allows bracket-key input to bypass arrayLimit and throwOnLimitExceeded when comma: true. The input a[]=1,2,3,4 succeeds with arrayLimit: 3, while the equivalent plain-key input is rejected.
Affected version tested:
Details
parseArrayValue() enforces the comma limit only for flat values. The a[] form is marked non-flat, so its comma-separated value is wrapped after parsing and the inner array is not checked. A single parameter can therefore materialize arbitrarily large arrays.
PoC
On v6.15.3, the first input parses successfully and the second creates an array with 1,000,001 elements. The equivalent a=1,2,3,4 input throws RangeError as expected.
Impact
An attacker who can supply a query string or form body can bypass configured array limits and force excessive memory allocation, causing denial of service. The limit must be applied after comma splitting and before the resulting array is wrapped.
Пакеты
qs
>= 6.14.2, <= 6.15.3
6.16.0
Связанные уязвимости
### Summary When `qs.parse` is called with `comma: true` and `throwOnLimitExceeded: true`, a comma-separated value under a bracket-push key (`a[]=1,2,3,4`) is split into an array without being compared against `arrayLimit`, while the same value under a flat key (`a=1,2,3,4`), an indexed key (`a[0]=`), a nested key (`a[b]=`), or a dotted key (`a.b=` with `allowDots`) throws the documented `RangeError`. A single parameter such as `a[]=1,2,2,...` therefore produces an inner array of arbitrary length even though the caller opted into the hard limit. This is the `[]=` key form that the fix for CVE-2026-2391 (qs 6.14.2) did not cover. ### Details In `lib/parse.js`, a comma-separated value under a `[]=` key is split and then wrapped as a single nested element (`val = [val]`, so that each `a[]=x,y` group counts as one element of the outer array). The `arrayLimit` check that 6.14.2 added for comma values runs after that wrap, so for `[]=` parts it only ever saw the wrapper of length 1. 6.15....
### Summary When `qs.parse` is called with `comma: true` and `throwOnLimitExceeded: true`, a comma-separated value under a bracket-push key (`a[]=1,2,3,4`) is split into an array without being compared against `arrayLimit`, while the same value under a flat key (`a=1,2,3,4`), an indexed key (`a[0]=`), a nested key (`a[b]=`), or a dotted key (`a.b=` with `allowDots`) throws the documented `RangeError`. A single parameter such as `a[]=1,2,2,...` therefore produces an inner array of arbitrary length even though the caller opted into the hard limit. This is the `[]=` key form that the fix for CVE-2026-2391 (qs 6.14.2) did not cover. ### Details In `lib/parse.js`, a comma-separated value under a `[]=` key is split and then wrapped as a single nested element (`val = [val]`, so that each `a[]=x,y` group counts as one element of the outer array). The `arrayLimit` check that 6.14.2 added for comma values runs after that wrap, so for `[]=` parts it only ever saw the wrapper of length 1. 6.15....
### Summary When `qs.parse` is called with `comma: true` and `throwOnLimitExceeded: true`, a comma-separated value under a bracket-push key (`a[]=1,2,3,4`) is split into an array without being compared against `arrayLimit`, while the same value under a flat key (`a=1,2,3,4`), an indexed key (`a[0]=`), a nested key (`a[b]=`), or a dotted key (`a.b=` with `allowDots`) throws the documented `RangeError`. A single parameter such as `a[]=1,2,2,...` therefore produces an inner array of arbitrary length even though the caller opted into the hard limit. This is the `[]=` key form that the fix for CVE-2026-2391 (qs 6.14.2) did not cover. ### Details In `lib/parse.js`, a comma-separated value under a `[]=` key is split and then wrapped as a single nested element (`val = [val]`, so that each `a[]=x,y` group counts as one element of the outer array). The `arrayLimit` check that 6.14.2 added for comma values runs after that wrap, so for `[]=` parts it only ever saw the wrapper of length 1.
### Summary When `qs.parse` is called with `comma: true` and `throw ...