Vulnerability-Lookup

CVE-2026-84997 (GCVE-0-2026-84997)

Vulnerability from cvelistv5 – Published: 2026-09-16 14:07 – Updated: 2026-09-16 14:46

Title

react/http: A malformed HTTP chunked body can lead to a denial-of-service and peg the CPU

Summary

react/http is an event-driven, streaming HTTP client and server implementation for ReactPHP. From 0.6.0 until 1.11.1, React\Http\Io\ChunkedDecoder could enter an infinite loop while processing a malformed Transfer-Encoding: chunked body because handleData required its buffer to shrink on every iteration. An incomplete terminal-chunk trailer without CRLF left the buffer unchanged after strpos returned false, and exactly two non-CRLF bytes after a completed non-terminal chunk bypassed both the error and wait guards. The affected decoder processes request bodies for React\Http\HttpServer and response bodies for React\Http\Browser, allowing a malicious client to freeze a server or a malicious or compromised server to freeze a client. A reverse proxy that normalizes inbound requests may protect the server direction but does not protect outbound Browser requests. This issue is fixed in version 1.11.1.

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: poc Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-16 14:46 UTC

CWE

CWE-835 - Loop with Unreachable Exit Condition ('Infinite Loop')

Assigner

GitHub_M mitre root

References

3 references

URL	Tags
https://github.com/reactphp/http/security/advisor…	x_refsource_CONFIRM
https://github.com/reactphp/http/commit/b6d468879…	x_refsource_MISC
https://github.com/reactphp/http/releases/tag/v1.11.1	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
reactphp	http	Affected: >= 0.6.0, < 1.11.1	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-84997

Vulnerability from fkie_nvd - Published: 2026-09-16 15:18 - Updated: 2026-09-16 15:18

Severity

7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/reactphp/http/commit/b6d4688790adf3797071fcf88a3fc4225f30486a
	security-advisories@github.com	https://github.com/reactphp/http/releases/tag/v1.11.1
	security-advisories@github.com	https://github.com/reactphp/http/security/advisories/GHSA-x424-64qh-5j54
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/reactphp/http/security/advisories/GHSA-x424-64qh-5j54

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "http",
          "vendor": "reactphp",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 0.6.0, \u003c 1.11.1"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
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    {
      "lang": "en",
      "value": "react/http is an event-driven, streaming HTTP client and server implementation for ReactPHP. From 0.6.0 until 1.11.1, React\\Http\\Io\\ChunkedDecoder could enter an infinite loop while processing a malformed Transfer-Encoding: chunked body because handleData required its buffer to shrink on every iteration. An incomplete terminal-chunk trailer without CRLF left the buffer unchanged after strpos returned false, and exactly two non-CRLF bytes after a completed non-terminal chunk bypassed both the error and wait guards. The affected decoder processes request bodies for React\\Http\\HttpServer and response bodies for React\\Http\\Browser, allowing a malicious client to freeze a server or a malicious or compromised server to freeze a client. A reverse proxy that normalizes inbound requests may protect the server direction but does not protect outbound Browser requests. This issue is fixed in version 1.11.1."
    }
  ],
  "id": "CVE-2026-84997",
  "lastModified": "2026-09-16T15:18:00.863",
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          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
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GHSA-X424-64QH-5J54

Vulnerability from github – Published: 2026-09-17 20:32 – Updated: 2026-09-17 20:32

Summary

react/http: A malformed HTTP chunked body can lead to a denial-of-service and peg the CPU

Details

Summary

A malformed HTTP message using Transfer-Encoding: chunked can drive React\Http\Io\ChunkedDecoder into an infinite loop, pegging a CPU core and freezing the event loop. Because ReactPHP is single-threaded, one such message stalls the entire process for every client until it is killed.

Both directions are affected. ChunkedDecoder decodes chunked request bodies for React\Http\HttpServer and chunked response bodies for React\Http\Browser, so a server can be attacked by a malicious client and a client can be attacked by a malicious or compromised server.

Details

ChunkedDecoder::handleData() loops while ($this->buffer !== '') and relies on the buffer shrinking each iteration. Two states leave the buffer unchanged while the loop condition stays true.

Terminal-chunk trailer. After the terminating 0 chunk, any remaining buffer is treated as trailer data to skip:

} elseif ($this->chunkSize === 0) {
    $this->buffer = (string)\substr($this->buffer, $positionCrlf);
}

When the trailer holds no CRLF yet, strpos() returns false, PHP coerces that to 0 in substr(), and the buffer is never advanced. Neither the error guard (which requires a non-zero chunk size) nor the wait guard (which requires fewer than two bytes remaining) can fire, so the loop re-enters with identical state.

Off-by-one after a completed chunk. Once a non-terminal chunk has been fully transferred, the "chunk does not end with a CRLF" error guard requires strlen($this->buffer) > 2 while the wait guard requires < 2. Exactly two non-CRLF bytes slip past both, and because the chunk is already complete nothing is consumed on the next iteration.

PoC

Run the example server from the reactphp/reactphp README and send a malformed request. Note the missing trailing \r\n:

POST / HTTP/1.1\r\nHost: x\r\nTransfer-Encoding: chunked\r\n\r\n0\r\nab

The PHP process pegs at 100% CPU and stops answering legitimate requests. A body of 1\r\nAAB triggers the second state.

The client side is reachable the same way: a Browser request to a server that answers with Transfer-Encoding: chunked and either malformed body shape hangs the client process.

Impact

Denial of service. The affected process stops responding entirely and has to be killed.

Servers behind a reverse proxy that parses and re-frames HTTP, such as a typical nginx setup, are not affected on the server side, because the proxy normalises the request before it reaches PHP. That mitigation does not extend to the client side: outbound requests made with Browser reach the remote server directly, so an application fetching attacker-influenced URLs is affected regardless of what sits in front of it.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.11.0"
      },
      "package": {
        "ecosystem": "Packagist",
        "name": "react/http"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.6.0"
            },
            {
              "fixed": "1.11.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-84997"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-835"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-17T20:32:39Z",
    "nvd_published_at": "2026-09-16T15:18:00Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\nA malformed HTTP message using `Transfer-Encoding: chunked` can drive `React\\Http\\Io\\ChunkedDecoder` into an infinite loop, pegging a CPU core and freezing the event loop. Because ReactPHP is single-threaded, one such message stalls the entire process for every client until it is killed.\n\nBoth directions are affected. `ChunkedDecoder` decodes chunked **request** bodies for `React\\Http\\HttpServer` and chunked **response** bodies for `React\\Http\\Browser`, so a server can be attacked by a malicious client and a client can be attacked by a malicious or compromised server.\n\n### Details\n\n`ChunkedDecoder::handleData()` loops `while ($this-\u003ebuffer !== \u0027\u0027)` and relies on the buffer shrinking each iteration. Two states leave the buffer unchanged while the loop condition stays true.\n\n**Terminal-chunk trailer.** After the terminating `0` chunk, any remaining buffer is treated as trailer data to skip:\n\n```php\n} elseif ($this-\u003echunkSize === 0) {\n    $this-\u003ebuffer = (string)\\substr($this-\u003ebuffer, $positionCrlf);\n}\n```\n\nWhen the trailer holds no CRLF yet, `strpos()` returns `false`, PHP coerces that to `0` in `substr()`, and the buffer is never advanced. Neither the error guard (which requires a non-zero chunk size) nor the wait guard (which requires fewer than two bytes remaining) can fire, so the loop re-enters with identical state.\n\n**Off-by-one after a completed chunk.** Once a non-terminal chunk has been fully transferred, the \"chunk does not end with a CRLF\" error guard requires `strlen($this-\u003ebuffer) \u003e 2` while the wait guard requires `\u003c 2`. Exactly two non-CRLF bytes slip past both, and because the chunk is already complete nothing is consumed on the next iteration.\n\n### PoC\n\nRun the example server from the `reactphp/reactphp` README and send a malformed request. Note the missing trailing `\\r\\n`:\n\n```\nPOST / HTTP/1.1\\r\\nHost: x\\r\\nTransfer-Encoding: chunked\\r\\n\\r\\n0\\r\\nab\n```\n\nThe PHP process pegs at 100% CPU and stops answering legitimate requests. A body of `1\\r\\nAAB` triggers the second state.\n\nThe client side is reachable the same way: a `Browser` request to a server that answers with `Transfer-Encoding: chunked` and either malformed body shape hangs the client process.\n\n### Impact\n\nDenial of service. The affected process stops responding entirely and has to be killed.\n\nServers behind a reverse proxy that parses and re-frames HTTP, such as a typical nginx setup, are not affected on the **server** side, because the proxy normalises the request before it reaches PHP. That mitigation does not extend to the **client** side: outbound requests made with `Browser` reach the remote server directly, so an application fetching attacker-influenced URLs is affected regardless of what sits in front of it.",
  "id": "GHSA-x424-64qh-5j54",
  "modified": "2026-09-17T20:32:39Z",
  "published": "2026-09-17T20:32:39Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/reactphp/http/security/advisories/GHSA-x424-64qh-5j54"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-84997"
    },
    {
      "type": "WEB",
      "url": "https://github.com/reactphp/http/commit/b6d4688790adf3797071fcf88a3fc4225f30486a"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FriendsOfPHP/security-advisories/blob/master/react/http/CVE-2026-84997.yaml"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/reactphp/http"
    },
    {
      "type": "WEB",
      "url": "https://github.com/reactphp/http/releases/tag/v1.11.1"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "react/http: A malformed HTTP chunked body can lead to a denial-of-service and peg the CPU"
}

Sightings

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Action not permitted

CVE-2026-84997 (GCVE-0-2026-84997)

FKIE_CVE-2026-84997

GHSA-X424-64QH-5J54

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