CVE-2026-104827: react/http unbounded response header buffering DoS

CVE-2026-104827 · Severity: high · CVSS 7.5 · Published 2026-10-15

React/Http is a PHP library used by applications to make HTTP requests to remote servers. An attacker controlling a remote HTTP server can send an incomplete response header and indefinitely stream data without finishing it, causing the client application to buffer all that data in memory until the process crashes. This is a network-based denial of service against any application that fetches URLs from untrusted sources, including through automatic redirects.

Technologies: react/http (Packagist). Vendors: Packagist.

Quick answers

Is CVE-2026-104827 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-104827 being exploited in the wild.
How severe is CVE-2026-104827?
High severity, with a CVSS score of 7.5, published 15 October 2026.
Which products and versions are affected?
react/http (Packagist) >= 1.0.0, <= 1.11.0, ECOSYSTEM:introduced=1.0.0,fixed=1.11.1.
Is there a fix for CVE-2026-104827?
Yes. react/http (Packagist): upgrade to 1.11.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-104827 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-104827?
Check whether you run react/http (Packagist) or ReactPHP React/Http at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • react/http (Packagist): upgrade to 1.11.1 or later
    composer require react/http:^1.11.1

Technical details

The vulnerability exists in ClientRequestStream::handleData(), which appends incoming bytes to an internal buffer without checking its size while waiting for the HTTP header terminator (\r\n\r\n or \n\n). An unauthenticated attacker can craft an HTTP response that withholds the terminator and sends data indefinitely, exhausting the client's memory until PHP's memory_limit is exceeded and the process crashes. The library already implements header size limits in other contexts (request headers when acting as a server, response body buffering), but not for response header reception.

Affected products

  • ReactPHP react/http

Identifiers

  • CVE-2026-104827
  • GHSA-g4f2-2pf3-2pwj

Timeline

  • 2026-10-15: disclosed

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