How severe is GHSA-mwv9-gp5h-frr4?

No CVSS score has been assigned to GHSA-mwv9-gp5h-frr4 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-mwv9-gp5h-frr4?

GHSA-mwv9-gp5h-frr4 affects the following packages: devalue (npm). Ecosystems affected: npm.

How do I fix GHSA-mwv9-gp5h-frr4?

Update devalue to 5.6.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mwv9-gp5h-frr4 is resolved across your whole dependency graph.

How do I detect GHSA-mwv9-gp5h-frr4 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for devalue, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-mwv9-gp5h-frr4 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is GHSA-mwv9-gp5h-frr4 actively exploited in the wild?

No public exploit code has been indexed for GHSA-mwv9-gp5h-frr4 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

When was GHSA-mwv9-gp5h-frr4 published, and has it been updated?

GHSA-mwv9-gp5h-frr4 was published on March 12, 2026 and was last updated on June 26, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

Sveltejs devalue's `devalue.parse` and `devalue.unflatten` emit objects with `proto` own propertiesGHSA-mwv9-gp5h-frr4

Fix: sveltejs/devalue@87c1f3c

GHSA-mwv9-gp5h-frr4 is a security vulnerability in devalue. A fix is available for devalue — see the affected versions and patch details below.

Published

Mar 12, 2026

Updated

Jun 26, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Jun 26, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

396other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

devaluenpm

24.9Mdownloads / week

Description

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

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`devalue`	≥ 4.0.0&&< 5.6.4	5.6.4`npm install devalue@5.6.4`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for devalue, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update devalue to 5.6.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mwv9-gp5h-frr4 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

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

O3 Security · Impact-Aware SCA

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Sveltejs devalue's `devalue.parse` and `devalue.unflatten` emit objects with `__proto__` own propertiesGHSA-mwv9-gp5h-frr4