CVE-2026-53666
Description
A flaw was found in React Router. If an application is configured to allow attacker-supplied input to modify errors during server-side rendering (SSR), a remote attacker could trigger unexpected code execution on the client. This execution could lead to an outbound network request, potentially resulting in limited information disclosure or unintended network activity. This vulnerability specifically affects applications utilizing Framework Mode and Data Mode with manual SSR/hydration.
Statement
This Moderate impact flaw in React Router affects applications configured to allow attacker-controlled input to modify server-side rendering (SSR) errors. Exploitation requires specific application-layer code in Framework Mode or Data Mode with manual SSR/hydration, leading to unexpected client-side code execution and potential outbound network requests for limited information disclosure or unintended network activity.
Mitigation
To mitigate this issue, ensure that custom application code does not permit attacker-controlled input to modify error objects during server-side rendering (SSR) when using React Router in Framework or Data Modes. Review and harden application-layer error handling to prevent such overwrites. Applications not requiring Framework or Data Mode SSR should consider utilizing Declarative Mode, which is unaffected.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.1 | N/A | 6.1 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | Required | N/A | Required |
| Scope | Changed | N/A | Changed |
| Confidentiality | Low | N/A | Low |
| Integrity Impact | Low | N/A | Low |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Application Data; Unexpected State
Attackers can modify unexpected objects or data that was assumed to be safe from modification. Deserialized data or code could be modified without using the provided accessor functions, or unexpected functions could be invoked.
Availability
Technical Impact: DoS: Resource Consumption (CPU)
If a function is making an assumption on when to terminate, based on a sentry in a string, it could easily never terminate.
Other
Technical Impact: Varies by Context
The consequences can vary widely, because it depends on which objects or methods are being deserialized, and how they are used. Making an assumption that the code in the deserialized object is valid is dangerous and can enable exploitation. One example is attackers using gadget chains to perform unauthorized actions, such as generating a shell.
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