# CVE-2026-123565: Devalue before 5.9.3 Quadratic Expansion Denial of Service via uneval


- **Severity:** High 8.7 (`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`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 8 Nov 2026
- **Updated:** 10 Nov 2026
- **Also known as:** CLSA-2026-1790939353, CLSA-2026-1793098685, GHSA-m5fj-453c-wwq4, GHSA-mcm9-63f2-9j32

## What is CVE-2026-123565?

CVE-2026-123565 is a high-severity vulnerability in sveltejs devalue, published on 8 Nov 2026. 

### Official description

Sveltejs devalue before 5.9.3 contains a resource exhaustion vulnerability where repeated primitive strings cause quadratic expansion in the uneval function. Attackers can supply a small crafted payload that is parsed and then passed to uneval, producing a very large serialized string that exhausts memory or CPU.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-123565?

1 open source package ship an affected version, including devalue.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `devalue` | npm | All versions | 5.9.3 |

## How do I fix CVE-2026-123565?

Upgrade devalue to 5.9.3 or later.

## Is CVE-2026-123565 being exploited?

There is no known exploitation of CVE-2026-123565 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-123565 and fix it if it is affected.

What it is: CVE-2026-123565 is a high-severity vulnerability in sveltejs devalue, published on 8 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-123565 in the wild and no public exploit code.

Affected packages and fixed versions:
- devalue (npm): affected all versions; fixed in 5.9.3

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-123565/ (Markdown: https://insights.sbomify.com/CVE-2026-123565/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-123565
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-123565
- OSV: https://osv.dev/vulnerability/CVE-2026-123565

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-123565/
Summaries are generated and may contain mistakes; the official description above is the record.