Quick answers
- Is CVE-2026-123565 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-123565 being exploited in the wild.
- How severe is CVE-2026-123565?
- High severity, with a CVSS score of 7.5, published 8 November 2026.
- Which products and versions are affected?
- Sveltejs Devalue before 5.9.3.
- Is there a fix for CVE-2026-123565?
- Yes: fixed in 5.9.3. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-123565 attacked?
- It is attacked over the network.
- Am I affected by CVE-2026-123565?
- Check whether you run Sveltejs Devalue at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- Fixed in: 5.9.3
Technical details
The vulnerability exists in the uneval function, where repeated primitive strings trigger quadratic expansion in the serialization process. An attacker can craft a small payload, have it parsed and passed to uneval, which generates a disproportionately large output. This is a denial-of-service attack requiring only network access with no authentication or user interaction needed.
Affected products
- Sveltejs devalue before 5.9.3
Timeline
- 2026-09-18: disclosed
- 2026-11-08: advisory