CVE-2026-123561 json
Sveltejs devalue before 5.9.3 __proto__ Rejection Bypass via Property-Key Coercion
published last mo. modified yesterday also EUVD-2026-119446 , GHSA-4q55-j62x-fr9h
- cvss
- 3.7
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.2%
- EPSS 0.2% chance of exploitation in 30 days, percentile 16%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- npm devalue 5.9.3
- sveltejs devalue 5.9.3
Is CVE-2026-123561 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- yesterday
Exploit prediction
0.25% chance of exploitation in the next 30 days, higher than 16% of all scored CVEs (FIRST EPSS, 2026-11-11).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 4.0 | 6.3 | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N |
| CNA | 3.1 | 3.7 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N |
| CNA | 4.0 | 6.3 | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| npm | devalue | <5.9.3 |
5.9.3 |
Affected products
- sveltejs devalue
Classification
- Weakness
-
- CWE-1321 Improperly Controlled Modification of Object Prototype Attributes
References
-
github.com
/sveltejs/devalue/commit/9ec513072e31f45e60d44dad6f0dba9c92bb8675
web
-
github.com
/sveltejs/devalue/security/advisories/GHSA-4q55-j62x-fr9h
vendor-advisory, web, advisory
-
vulncheck.com
/advisories/sveltejs-devalue-before-5.9.3-proto-rejection-bypass-via-property-key-coercion
third-party-advisory
-
github.com
/sveltejs/devalue
package
-
github.com
/sveltejs/devalue/releases/tag/v5.9.3
web
Sources
- CVE List CVE-2026-123561
- GitHub Advisory GHSA-4q55-j62x-fr9h
- NVD CVE-2026-123561
- Maintainer advisory GHSA-4q55-j62x-fr9h
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.
The maintainers of sveltejs/devalue published their own advisory on GitHub. Reviewed sources take precedence over it.