CVE-2026-81176

Svelte devalue is a JavaScript library that serializes values into strings when JSON.stringify isn't sufficient for the job. Prior to 5.9.2, devalue.parse does not reject out-of-bounds indices that are greater than or equal to values.length in src/parse.js. A specially crafted untrusted payload can make the parser alternate between array representations, producing quadratic work as the payload grows and causing denial of service in applications that parse untrusted devalue data. This issue is fixed in version 5.9.2.

Svelte devalue is a JavaScript library that serializes values into strings when JSON.stringify isn't sufficient for the job. Prior to 5.9.2, devalue.parse does not reject out-of-bounds indices that are greater than or equal to values.length in src/parse.js. A specially crafted untrusted payload can make the parser alternate between array representations, producing quadratic work as the payload grows and causing denial of service in applications that parse untrusted devalue data. This issue is fixed in version 5.9.2.

Under certain circumstances, serializing sparse arrays using uneval or stringify could cause CPU and/or memory exhaustion. When this occurs on the server, it results in a DoS. This is extremely difficult to take advantage of in practice, as an attacker would have to manage to create a sparse array on the server — which is impossible in every mainstream wire format — and then that sparse array would have to be run through uneval or stringify.

Under certain circumstances, unevaling untrusted data can produce output code that will create objects with polluted prototypes when later evaled, meaning the output data can be a different shape from the input data.

Impact

devalue.parse prior to version 5.9.2 fails to reject out-of-bounds indices. Specially-crafted payloads can exploit this to cause devalue to alternate between different array representations, resulting in work that is quadratic with payload size.

Applications are potentially affected if they call devalue.parse with untrusted data.

Patches

The bug is fixed in [email protected].

In some circumstances, devalue.parse and devalue.unflatten could emit objects with __proto__ own properties. This in and of itself is not a security vulnerability (and is possible with, for example, JSON.parse as well), but it can result in prototype injection if downstream code handles it incorrectly:

const result = devalue.parse(/* input creating an object with a __proto__ property */);
const target = {};
Object.assign(target, result); // target's prototype is now polluted

TuxCare rebuilt devalue to address 2 CVEs. Fixed in 4.3.3-tuxcare.3.

TuxCare rebuilt devalue to address 2 CVEs. Fixed in 2.0.1-tuxcare.4.

TuxCare rebuilt devalue to address 5 CVEs. Fixed in 4.3.2-tuxcare.1.

TuxCare rebuilt devalue to address 1 CVE. Fixed in 4.3.2-tuxcare.2.

TuxCare rebuilt devalue to address 3 CVEs. Fixed in 4.3.3-tuxcare.5.

TuxCare rebuilt devalue to address 2 CVEs. Fixed in 4.3.2-tuxcare.3.

TuxCare rebuilt devalue to address 2 CVEs. Fixed in 4.3.0-tuxcare.2.

TuxCare rebuilt devalue to address 2 CVEs. Fixed in 4.3.1-tuxcare.2.

TuxCare rebuilt devalue to address 1 CVE. Fixed in 5.9.0-tuxcare.5.

TuxCare rebuilt devalue to address 2 CVEs. Fixed in 5.9.1-tuxcare.2.

TuxCare rebuilt devalue to address 7 CVEs. Fixed in 5.8.2-tuxcare.1.

TuxCare rebuilt devalue to address 6 CVEs. Fixed in 5.8.1-tuxcare.1.