CVE-2025-66456

Published Dec 9, 2025

Last updated a month ago

Overview

AI description

Automated description summarized from trusted sources.

CVE-2025-66456 refers to a critical remote code execution (RCE) vulnerability found in React Server Components (RSC), specifically within the Flight protocol. This vulnerability, initially tracked under CVE-2025-55182 (React) and CVE-2025-66478 (Next.js) (CVE-2025-66478 was later rejected as a duplicate of CVE-2025-55182), allows unauthenticated attackers to execute arbitrary code on the server. The flaw stems from insecure deserialization of malicious HTTP requests sent to React Server Function endpoints. Successful exploitation of CVE-2025-66456 enables attackers to influence server-side execution logic, leading to the execution of privileged JavaScript code on the server. It was reported that the exploit has near-100% reliability and requires no code changes to be effective against default configurations. A fix was introduced in React versions 19.0.1, 19.1.2, and 19.2.1.

Description: Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation and client-server communication. Versions 1.4.0 through 1.4.16 contain a prototype pollution vulnerability in `mergeDeep` after merging results of two standard schema validations with the same key. Due to the ordering of merging, there must be an any type that is set as a standalone guard, to allow for the `__proto__ prop` to be merged. When combined with GHSA-8vch-m3f4-q8jf this allows for a full RCE by an attacker. This issue is fixed in version 1.4.17. To workaround, remove the `__proto__ key` from body.
Source: security-advisories@github.com
NVD status: Analyzed
Products: elysia

Risk scores

CVSS 4.0

Type: Secondary
Base score: 9.1
Impact score: -
Exploitability score: -
Vector string: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/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
Severity: CRITICAL

CVSS 3.1

Type: Primary
Base score: 9.8
Impact score: 5.9
Exploitability score: 3.9
Vector string: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Severity: CRITICAL

Weaknesses

security-advisories@github.com: CWE-1321

Hype score: Not currently trending

Configurations

[
  {
    "nodes": [
      {
        "negate": false,
        "cpeMatch": [
          {
            "criteria": "cpe:2.3:a:elysiajs:elysia:*:*:*:*:*:node.js:*:*",
            "vulnerable": true,
            "matchCriteriaId": "41035CD2-DE13-469A-984F-6BC1CCCF2695",
            "versionEndExcluding": "1.4.17",
            "versionStartIncluding": "1.4.0"
          }
        ],
        "operator": "OR"
      }
    ]
  }
]

References

Sources include official advisories and independent security research.