CVE-2026-31865
Elysia Cookie Value Prototype Pollution
Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation, and client-server communication. Prior to version 1.4.27, an Elysia cookie can be overridden by prototype pollution , eg. __proto__. This issue is patched in 1.4.27. As a workaround, use t.Cookie validation to enforce validation value and/or prevent iterable over cookie if possible.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
Exploit likelihood
What each source reports
CVE List Score used
Elysia Cookie Value Prototype Pollution
Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation, and client-server communication. Prior to version 1.4.27, an Elysia cookie can be overridden by prototype pollution , eg. __proto__. This issue is patched in 1.4.27. As a workaround, use t.Cookie validation to enforce validation value and/or prevent iterable over cookie if possible.
- Record
CVE-2026-31865- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N - Weakness
- CWE-1321
- Updated
- 2026-11-02
EUVDEUVD-2026-12749
Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation, and client-server communication. Prior to version 1.4.27, an Elysia cookie can be overridden by prototype pollution , eg. __proto__. This issue is patched in 1.4.27. As a workaround, use t.Cookie validation to enforce validation value and/or prevent iterable over cookie if possible.
- Record
EUVD-2026-12749- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-8hq9-phh3-p2wp
Elysia Cookie Value Prototype Pollution
Impact
Elysia cookie can be overridden by prototype pollution , eg. __proto__
Sending cookie with the follows name can override cookie value:
__proto__=%7B%22injected%22%3A%22polluted%22%7D
Patches
Patched by 1.4.27
Workarounds
- Use t.Cookie validation to enforce validation value
- Prevent iterable over cookie if possible
- Record
GHSA-8hq9-phh3-p2wp- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N - Weakness
- CWE-1321
- Updated
- 2026-11-02
NVD
Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation, and client-server communication. Prior to version 1.4.27, an Elysia cookie can be overridden by prototype pollution , eg. __proto__. This issue is patched in 1.4.27. As a workaround, use t.Cookie validation to enforce validation value and/or prevent iterable over cookie if possible.
- Record
CVE-2026-31865- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N - CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N - Weakness
- CWE-1321
- Updated
- 2026-11-02
OSV
Elysia Cookie Value Prototype Pollution
Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation, and client-server communication. Prior to version 1.4.27, an Elysia cookie can be overridden by prototype pollution , eg. __proto__. This issue is patched in 1.4.27. As a workaround, use t.Cookie validation to enforce validation value and/or prevent iterable over cookie if possible.
- Record
CVE-2026-31865- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N - Weakness
- CWE-1321
- Updated
- 2026-11-02
OSVGHSA-8hq9-phh3-p2wp
Elysia Cookie Value Prototype Pollution
Impact
Elysia cookie can be overridden by prototype pollution , eg. __proto__
Sending cookie with the follows name can override cookie value:
__proto__=%7B%22injected%22%3A%22polluted%22%7D
Patches
Patched by 1.4.27
Workarounds
- Use t.Cookie validation to enforce validation value
- Prevent iterable over cookie if possible
- Record
GHSA-8hq9-phh3-p2wp- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N - Weakness
- CWE-1321
- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
elysianpm |
before 1.4.27 | 1.4.27 |
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | CVE List, EUVD, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-31865 is a medium vulnerability (CVSS 6.5) in Elysiajs Elysia, published March 17, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.25%, the 15th percentile. Fixed in elysia 1.4.27.
References
github.com/elysiajs/elysia/security/advisories/GHSA-8hq9-phh3-p2wp
nvd.nist.gov/vuln/detail/CVE-2026-31865