Quick answers
- Is CVE-2026-123563 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-123563 being exploited in the wild.
- How severe is CVE-2026-123563?
- High severity, with a CVSS score of 7.5, published 8 November 2026.
- Which products and versions are affected?
- Svelte Devalue before 5.9.3.
- Is there a fix for CVE-2026-123563?
- 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-2026-123563 attacked?
- It is attacked over the network.
- Am I affected by CVE-2026-123563?
- Check whether you run Svelte 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 is a memory allocation validation bypass (CWE-789) in the parse function where custom ArrayBuffer revivers can circumvent typed-array allocation checks. An attacker supplies crafted input with a malformed ArrayBuffer reviver that, despite small input size, triggers allocation of massive ArrayBuffers. This is a denial-of-service attack requiring only network access to a service using vulnerable Devalue versions; no authentication or user interaction is needed.
Affected products
- Svelte Devalue before 5.9.3
Timeline
- 2026-09-18: disclosed: GitHub Security Advisory GHSA-r9w8-h9r3-54w4 published
- 2026-11-08: advisory