LiquidJS: ownPropertyOnly bypass for inherited array indices in first/last/join/reverse/slice/compact, `.first`/`.last`, negative index, and for-loop iteration

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

LiquidJS is a Shopify / GitHub Pages compatible template engine in pure JavaScript. Prior to 10.27.2, enabling ownPropertyOnly does not consistently restrict inherited array indices because negative indexing, .first, .last, the first filter, the last filter, join, reverse, slice, compact, and for-loop iteration can read prototype-provided elements outside readJSProperty(). An attacker who can influence prototype state or inherited array-index data and cause templates to render affected operations can disclose values that ownPropertyOnly is expected to hide. Direct positive indexing and ordinary object prototype reads are blocked, but the alternate array paths remain affected. This issue is fixed in 10.27.2.

Source published

6 Oct 2026 18:04:14 UTC

Source modified

9 Oct 2026 01:22:05 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 6.0 CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

LiquidJS is a Shopify / GitHub Pages compatible template engine in pure JavaScript. Prior to 10.27.2, enabling ownPropertyOnly does not consistently restrict inherited array indices because negative indexing, .first, .last, the first filter, the last filter, join, reverse, slice, compact, and for-loop iteration can read prototype-provided elements outside readJSProperty(). An attacker who can influence prototype state or inherited array-index data and cause templates to render affected operations can disclose values that ownPropertyOnly is expected to hide. Direct positive indexing and ordinary object prototype reads are blocked, but the alternate array paths remain affected. This issue is fixed in 10.27.2.

Source published

Oct 6, 2026, 6:04:14 PM (timezone not stated)

Source modified

Oct 9, 2026, 1:22:05 AM (timezone not stated)

Observed here

9 Nov 2026 05:06:34 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 6.0 CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

LiquidJS is a Shopify / GitHub Pages compatible template engine in pure JavaScript. Prior to 10.27.2, enabling ownPropertyOnly does not consistently restrict inherited array indices because negative indexing, .first, .last, the first filter, the last filter, join, reverse, slice, compact, and for-loop iteration can read prototype-provided elements outside readJSProperty(). An attacker who can influence prototype state or inherited array-index data and cause templates to render affected operations can disclose values that ownPropertyOnly is expected to hide. Direct positive indexing and ordinary object prototype reads are blocked, but the alternate array paths remain affected. This issue is fixed in 10.27.2.

Source published

6 Oct 2026 19:17:42 UTC

Source modified

9 Oct 2026 02:16:57 UTC

Observed here

25 Oct 2026 04:17:41 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 6.0 CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

## Summary LiquidJS’s `ownPropertyOnly` option is intended to prevent templates from reading inherited or prototype properties from scope data. With `ownPropertyOnly: true`, direct access such as: ```liquid {{ a[0] }} ``` correctly blocks an inherited array index. However, the same inherited value is still disclosed through: ```text .first .last negative indexing for-loop iteration first last join reverse slice compact ``` ## Impact This is an information disclosure issue when an application relies on `ownPropertyOnly: true` to safely render templates over untrusted or prototype-polluted scope data. Object prototype property reads are blocked as expected, but inherited `Array.prototype` index reads are not consistently blocked. An attacker who can influence prototype state or inherited array-index data may cause templates to disclose values that `ownPropertyOnly` is expected to hide. ## Proof of concept ```js const { Liquid } = require("liquidjs"); const engine = new Liquid({ ownPropertyOnly: true }); Array.prototype[0] = "ARRAY_PROTO_POLLUTED"; Object.prototype.secret = "OBJECT_PROTO_POLLUTED"; const a = []; a.length = 1; const o = {}; for (const [src, scope] of [ ["{{ a[0] }}", { a }], ["{{ a[-1] }}", { a }], ["{{ o.secret }}", { o }], ["{{ a.first }}", { a }], ["{{ a.last }}", { a }], ["{{ a | first }}", { a }], ["{{ a | last }}", { a }], ["{{ a | join: ',' }}", { a }], ["{{ a | reverse | first }}", { a }], ["{{ a | slice: 0, 1 | join: ',' }}", { a }], ["{{ a | compact | join: ',' }}", { a }], ["{% for x in a %}[{{ x }}]{% endfor %}", { a }], ]) { console.log(src, "=>", JSON.stringify(engine.parseAndRenderSync(src, scope))); } delete Array.prototype[0]; delete Object.prototype.secret; ``` ## Observed behavior ```text {{ a[0] }} => "" {{ a[-1] }} => "ARRAY_PROTO_POLLUTED" {{ o.secret }} => "" {{ a.first }} => "ARRAY_PROTO_POLLUTED" {{ a.last }} => "ARRAY_PROTO_POLLUTED" {{ a | first }} => "ARRAY_PROTO_POLLUTED" {{ a | last }} => "ARRAY_PROTO_POLLUTED" {{ a | join: ',' }} => "ARRAY_PROTO_POLLUTED" {{ a | reverse | first }} => "ARRAY_PROTO_POLLUTED" {{ a | slice: 0, 1 | join: ',' }} => "ARRAY_PROTO_POLLUTED" {{ a | compact | join: ',' }} => "ARRAY_PROTO_POLLUTED" {% for x in a %}[{{ x }}]{% endfor %} => "[ARRAY_PROTO_POLLUTED]" ``` ## Expected behavior When `ownPropertyOnly: true` is enabled, inherited array indices should be treated as absent, matching the behavior of: ```liquid {{ a[0] }} {{ o.secret }} ``` Inherited or prototype-provided array-index values should not be exposed through array filters, array properties, negative indexing, or loop iteration. ## Root cause `ownPropertyOnly` appears to be enforced in `readJSProperty()`, but several array-element access paths use raw or native array operations instead. Examples include: ```text negative indexing using obj[obj.length + key] readFirst/readLast using obj[0] / obj[obj.length - 1] filters such as first, last, join, reverse, slice, and compact operating on arrays through native element reads for-loop iteration materializing inherited array indices ``` Because these paths do not consistently check whether an array index is an own property, inherited array indices can be read even when `ownPropertyOnly` is enabled.

Source published

7 Oct 2026 16:19:09 UTC

Source modified

7 Oct 2026 16:30:04 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Publisher rating · MODERATE