CVSS 4.0
6.3 mediumCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:NCVE-2026-123561
Medium (6.3) in sveltejs devalue. EPSS 0.2% estimated probability of exploitation activity in the next 30 days. Fixed in devalue 5.9.3.
On this page
devalue before 5.9.3 allows malformed null-prototype object keys to bypass parse's __proto__ rejection through property-key coercion, an incomplete fix for GHSA-mwv9-gp5h-frr4. Attackers can supply crafted payloads that yield objects with a __proto__ own property, which alone does not cause prototype pollution.
Severity
CVSS 3.1
3.7 lowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N- EPSS
- 0.2% estimated probability of exploitation activity in the next 30 days; 16th percentile. Scored 2026-11-10. A forecast for this CVE across the internet, not for your own systems.
- CWE
- CWE-1321 Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution)
- Published
- NVD analysis
- Awaiting analysis
- Record from
- the NVD, synced
Ask an AI about this CVE
Show the prompt
Explain CVE-2026-123561 for an engineer deciding whether to act. Use https://cve.bz/api/public/cves/CVE-2026-123561?via=ask-ai-copy and https://cve.bz/cve/CVE-2026-123561?via=ask-ai-copy as the source of truth: what is affected and which versions fix it, whether it is in CISA KEV, public exploits, and its EPSS (an internet-wide 30-day estimate of exploitation activity, not a forecast for my systems). If they give no fixed versions, use the CVE record https://cveawg.mitre.org/api/cve/CVE-2026-123561 or the vendor advisory, not third-party mirrors. Tell me how to check whether I am affected and how to verify a fix. Cite the sources and say where they are uncertain.Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this CVE's id and public links.
Affected
Versions
From the CNA's record in the CVE List.
| Product | Affected |
|---|---|
| sveltejs devalue | before 5.9.3 |
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-4q55-j62x-fr9h | npm | devalue | <5.9.3 | 5.9.3 |
Attack patterns (CAPEC)
- CAPEC-1 Accessing Functionality Not Properly Constrained by ACLs Likelihood: High · Severity: High
- CAPEC-77 Manipulating User-Controlled Variables Likelihood: High · Severity: Very High
- CAPEC-180 Exploiting Incorrectly Configured Access Control Security Levels Likelihood: High · Severity: Medium
The attack patterns MITRE's CAPEC relates to this record's weaknesses, as MITRE names them. Credits.