Web

CVE-2026-123564

8.7

High

EPSS 0.34%Patch available

Memory exhaustion via uneval of large sparse arrays in sveltejs devalue (<5.9.3)

exploited

No known exploitation not in CISA KEV as of our last sync

fix

Fixed in 5.9.3

likelihood

EPSS 0.34%top 72% of scored CVEs

Published 8 Nov 2026Analysed here 8 Nov 2026CVSS scored by the publisher (CNA)

do firstUpgrade to a fixed release: 5.9.3.

common questions

Is CVE-2026-123564 being exploited?

Not confirmed. CVE-2026-123564 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.34% probability of exploitation in the next 30 days.

How severe is CVE-2026-123564?

CVE-2026-123564 is rated High with a CVSS score of 8.7. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.

Is there a patch for CVE-2026-123564?

Yes. A fix has been recorded for CVE-2026-123564. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.

What does CVE-2026-123564 affect?

CVE-2026-123564 affects sveltejs devalue <5.9.3, Svelte-based web applications, Browsers evaluating uneval output, Node.js runtimes evaluating uneval. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.

What should I do about CVE-2026-123564?

Upgrade devalue to >=5.9.3 and sanitize/limit serialized array sizes.

Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.

executive summary

technical analysis

affected

sveltejs devalue <5.9.3Svelte-based web applicationsBrowsers evaluating uneval outputNode.js runtimes evaluating uneval

impact

Remote memory exhaustion (DoS) by attacker-influenced sparse arrays in uneval-generated code, crashing browsers or Node.js runtimes.

action required

Patch when possible

affected versions

sveltejs devalue

affected>= 1.0.0 and < 5.9.3

vendor says fixed in5.9.3

As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.

timeline

8 Nov 2026Published
8 Nov 2026CVE record last updated · same day later
8 Nov 2026Analysed by vulneraibility.com · 1 day later

also known as

GHSA-wf3x-273g-mvxv

how to fix

Remediation steps are tailored for users whose stack is affected. Add this technology to your stack to see the fix checklist.

references

NVD CVE.org CVE Details Source

2 references in the CVE record: 2 advisories

Advisorygithub.com /sveltejs/devalue/security/advisories/GHSA-wf3x-273g-mvxv
Advisoryvulncheck.com /advisories/sveltejs-devalue-before-5.9.3-memory-exhaustion-via-uneval-sparse-ar

sources

CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
NVD: CVSS and CPE data
FIRST EPSS: exploit probability and percentile
OSV: advisory aliases and downstream package versions
Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.

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