{"id":"UBUNTU-CVE-2026-82562","details":"### 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. 6.15.3 added a pre-split comma count so that an oversized value throws before it is allocated, but gated it on an `isFlatArrayValue` flag that `parseValues` set to `false` for any part containing `[]=`, and did not pass it for object-valued input, so the gap remained. #### PoC ```js var qs = require('qs'); var options = { comma: true, arrayLimit: 3, throwOnLimitExceeded: true }; qs.parse('a=1,2,3,4', options);   // RangeError: Array limit exceeded. Only 3 elements allowed in an array. qs.parse('a[]=1,2,3,4', options); // { a: [ [ '1', '2', '3', '4' ] ] }  (no throw) qs.parse('a[]=' + '1,'.repeat(1000000) + '1', { comma: true, arrayLimit: 20, throwOnLimitExceeded: true }); // no throw; a 1,000,001-element inner array is allocated ``` #### Fix `lib/parse.js`, applied in 8859c37 on `main` and released as v6.16.0: the `isFlatArrayValue` gate is removed, so every comma-split value is counted against `arrayLimit` before splitting regardless of key form. An in-limit group under `a[]=` still counts as one element of the outer array, and the default (`throwOnLimitExceeded: false`) path is unchanged. ### Affected versions `\u003e=6.14.2 \u003c6.16.0`, fixed in v6.16.0. v6.14.2 introduced `arrayLimit` enforcement for comma values (the fix for CVE-2026-2391) but only for values not under a `[]=` key, and every release from v6.14.2 through v6.15.3 has the same gap. v6.14.0 and v6.14.1, where `throwOnLimitExceeded` exists but does not apply to any comma form, are covered by CVE-2026-2391 rather than this record. Earlier lines (6.7.x through 6.13.x) have `comma` but no `throwOnLimitExceeded`, so there is no hard cap on any comma path to bypass; releases before 6.7.0 have no `comma` option. ### Impact An unauthenticated attacker who can reach an application that parses untrusted query strings or urlencoded bodies with both `comma: true` and `throwOnLimitExceeded: true` (both non-default) can bypass the configured limit with a single `a[]=` parameter and force the parser to allocate an array proportional to the request size. The cost is strictly linear in the attacker-supplied bytes (about 0.1 microseconds and 6 to 7 retained bytes per input byte; the same out-of-memory threshold as the documented default `throwOnLimitExceeded: false` path), so a transport-layer request or body size limit bounds it completely (and node's default maximum HTTP header size of 16 KB already bounds the request line, so multi-megabyte payloads need a body parser). The impact is that an opt-in hard limit fails open on one key spelling, not unbounded allocation from a small input.","modified":"2026-09-02T16:28:28Z","published":"2026-08-30T01:20:00Z","upstream":["CVE-2026-82562"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-82562"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-82562"},{"type":"REPORT","url":"https://github.com/ljharb/qs/security/advisories/GHSA-x5fp-wj9c-mxmx"},{"type":"REPORT","url":"https://github.com/ljharb/qs/commit/8859c37470e11b42b547b275e4e9bd0bc8cc5464"},{"type":"REPORT","url":"https://github.com/ljharb/qs/security/advisories/GHSA-w7fw-mjwx-w883"}],"affected":[{"package":{"name":"node-qs","ecosystem":"Ubuntu:Pro:14.04:LTS","purl":"pkg:deb/ubuntu/node-qs?arch=source&distro=esm-infra-legacy%2Ftrusty"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.4.2-1","0.6.5-1","0.6.5-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"node-qs","binary_version":"0.6.5-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-82562.json"}},{"package":{"name":"node-qs","ecosystem":"Ubuntu:16.04:LTS","purl":"pkg:deb/ubuntu/node-qs?arch=source&distro=xenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.4-1"],"ecosystem_specific":{"binaries":[{"binary_name":"node-qs","binary_version":"2.2.4-1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-82562.json"}},{"package":{"name":"node-qs","ecosystem":"Ubuntu:18.04:LTS","purl":"pkg:deb/ubuntu/node-qs?arch=source&distro=bionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.4-1","2.2.4-1ubuntu1"],"ecosystem_specific":{"binaries":[{"binary_name":"node-qs","binary_version":"2.2.4-1ubuntu1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-82562.json"}},{"package":{"name":"node-qs","ecosystem":"Ubuntu:Pro:20.04:LTS","purl":"pkg:deb/ubuntu/node-qs?arch=source&distro=esm-apps%2Ffocal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.5.2-1","6.9.0+ds-1","6.9.1+ds-1","6.9.1+ds-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_version":"6.9.1+ds-1ubuntu0.1~esm1","binary_name":"node-qs"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-82562.json"}},{"package":{"name":"node-qs","ecosystem":"Ubuntu:22.04:LTS","purl":"pkg:deb/ubuntu/node-qs?arch=source&distro=jammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.9.4+ds-1","6.10.1+ds-1","6.10.2+ds+~6.9.7-1","6.10.3+ds+~6.9.7-1"],"ecosystem_specific":{"binaries":[{"binary_name":"node-qs","binary_version":"6.10.3+ds+~6.9.7-1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-82562.json"}},{"package":{"name":"node-qs","ecosystem":"Ubuntu:24.04:LTS","purl":"pkg:deb/ubuntu/node-qs?arch=source&distro=noble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.11.0+ds+~6.9.7-3","6.11.0+ds+~6.9.7-4"],"ecosystem_specific":{"binaries":[{"binary_name":"node-qs","binary_version":"6.11.0+ds+~6.9.7-4"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-82562.json"}},{"package":{"name":"node-qs","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/node-qs?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.13.0+ds+~6.9.16-1","6.14.1+ds+~6.14.0-1"],"ecosystem_specific":{"binaries":[{"binary_version":"6.14.1+ds+~6.14.0-1","binary_name":"node-qs"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-82562.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"},{"type":"Ubuntu","score":"medium"}]}