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The vulnerability resides in the `websocket-driver` library, a WebSocket protocol handler widely used in Node.js environments. Prior to version 0.7.5, the implementation of the legacy draft-75/76 WebSocket frame parsing within `lib/websocket/driver/draft75.js` contains a critical flaw in how it processes the length header of incoming frames.
In the WebSocket draft protocol, the length of a frame’s payload is not transmitted as a fixed-size field. Instead, it is encoded as a variable-length sequence of bytes where the high bit (0x80) of each byte indicates that more bytes follow. The lower 7 bits of each byte contribute to the final integer value. This encoding allows an arbitrarily large integer to be represented, but the `draft75.js` parser does not impose any upper bound on the accumulated value.
An attacker can exploit this by sending a continuous stream of bytes, each with a value of `0x80` or higher (e.g., 0x80, 0x81, 0xFF). The parser reads these bytes in a loop, repeatedly shifting and adding bits to construct the length integer. Because JavaScript represents all numbers as 64-bit floating-point values (IEEE 754 double-precision), this integer will eventually exceed the safe integer limit (2^53 - 1). At this point, the number loses precision, and the parser’s calculation of the frame boundary becomes corrupted.
This corruption causes the parser to misinterpret the boundaries of subsequent data frames. The result is that the payload of the current frame and the framing of following messages are parsed incorrectly. This can lead to a complete breakdown of the WebSocket connection, message corruption, or a denial-of-service condition where the server is unable to process legitimate traffic. The vulnerability is particularly dangerous because it can be triggered by a single malicious client and does not require any special privileges.
The fix in version 0.7.5 addresses this by implementing a strict check: the parser now closes the connection as soon as the accumulated length exceeds the configured maximum message length. This prevents the integer from growing indefinitely and eliminates the precision loss issue. An additional post-extension size check was also added to the RFC 6455 path in `hybi.js` for broader protection.
DailyCVE Form:
Platform: Node.js library
Version: < 0.7.5
Vulnerability: Integer overflow
Severity: Critical
date: 2026-07-17
Prediction: 2026-07-20
What Undercode Say:
Analytics indicate that this vulnerability affects any application using `websocket-driver` versions prior to 0.7.5, often as a transitive dependency through tools like webpack-dev-server, sockjs, and faye-websocket. Dependency scanners are flagging this issue widely, as the vulnerable code path is triggered by any client that sends a maliciously crafted WebSocket frame. The attack is trivial to execute and requires minimal bandwidth, making it a high-priority item for remediation.
Check current version npm list websocket-driver Identify vulnerable dependencies (example output) └─┬ [email protected] └─┬ [email protected] └─┬ [email protected] └── [email protected] Update to patched version npm update websocket-driver Force upgrade to 0.7.5 or higher npm install [email protected] --save For lockfile-only refresh (if constraint allows) npm update websocket-driver
Exploit:
An attacker can exploit this vulnerability by establishing a WebSocket connection and sending a frame with a malformed length header. The frame begins with a byte indicating the start of the length field. The attacker then sends an indefinite sequence of bytes, each with the high bit set (e.g., 0x80). The server’s `draft75.js` parser will continuously accumulate these bytes into an integer, eventually losing precision and misinterpreting the frame boundary. This can cause the server to hang, crash, or process subsequent data incorrectly. No authentication or special network position is required; the attacker only needs to be able to send WebSocket frames to the target server.
Protection:
The primary and only complete protection is to upgrade to `websocket-driver` version 0.7.5 or later. This version introduces a hard cap on the accumulated length, immediately closing the connection if the value exceeds the configured maximum message size. For applications that cannot upgrade immediately, consider removing or disabling the use of the vulnerable `draft75.js` parser if possible, though this may break compatibility with older clients. Network-level controls such as WebSocket proxy filtering or rate-limiting can help mitigate the impact of an attack, but they do not fix the underlying parsing flaw. Regularly scanning dependencies with tools like `npm audit` or Snyk is recommended to detect and remediate such issues early.
Impact:
Successful exploitation leads to a denial-of-service condition where the WebSocket server becomes unable to correctly parse incoming messages. This can result in connection resets, application freezes, or memory exhaustion as the parser attempts to handle the corrupted data. In some scenarios, the loss of precision may cause the server to misinterpret the boundaries of subsequent frames, potentially leading to data corruption or security controls being bypassed. The vulnerability is rated as Critical due to its ease of exploitation, the low complexity of the attack, and the potential for widespread disruption in applications that rely on WebSocket communication.
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Sources:
Reported By: nvd.nist.gov
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