CVE-2016-10536
Insecure Defaults Allow MITM Over TLS in engine.io-client
CVE-2016-10536 is a medium vulnerability (CVSS 5.9) in Socket Engine.io-client, published May 31, 2018. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.00%, the 62nd percentile. Fixed in engine.io-client 1.6.9.
engine.io-client is the client for engine.io, the implementation of a transport-based cross-browser/cross-device bi-directional communication layer for Socket.IO. The vulnerability is related to the way that node.js handles the rejectUnauthorized setting. If the value is something that evaluates to false, certificate verification will be disabled. This is problematic as engine.io-client 1.6.8 and earlier passes in an object for settings that includes the rejectUnauthorized property, whether it has been set or not. If the value has not been explicitly changed, it will be passed in as null, resulting in certificate verification being turned off.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- High
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- High
- Integrity
- None
- Availability
- None
Exploit likelihood
What each source reports
NVD Score used
engine.io-client is the client for engine.io, the implementation of a transport-based cross-browser/cross-device bi-directional communication layer for Socket.IO. The vulnerability is related to the way that node.js handles the rejectUnauthorized setting. If the value is something that evaluates to false, certificate verification will be disabled. This is problematic as engine.io-client 1.6.8 and earlier passes in an object for settings that includes the rejectUnauthorized property, whether it has been set or not. If the value has not been explicitly changed, it will be passed in as null, resulting in certificate verification being turned off.
- Record
CVE-2016-10536- CVSS 3.0
- 5.9 Medium
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N - CVSS 2.0
- 4.3 Medium
AV:N/AC:M/Au:N/C:P/I:N/A:N - Weakness
- CWE-300, CWE-295
- Updated
- 2026-11-02
CVE List No score
engine.io-client is the client for engine.io, the implementation of a transport-based cross-browser/cross-device bi-directional communication layer for Socket.IO. The vulnerability is related to the way that node.js handles the rejectUnauthorized setting. If the value is something that evaluates to false, certificate verification will be disabled. This is problematic as engine.io-client 1.6.8 and earlier passes in an object for settings that includes the rejectUnauthorized property, whether it has been set or not. If the value has not been explicitly changed, it will be passed in as null, resulting in certificate verification being turned off.
- Record
CVE-2016-10536- Weakness
- CWE-300
- Updated
- 2026-11-02
EUVDEUVD-2019-0221 No score
engine.io-client is the client for engine.io, the implementation of a transport-based cross-browser/cross-device bi-directional communication layer for Socket.IO. The vulnerability is related to the way that node.js handles the rejectUnauthorized setting. If the value is something that evaluates to false, certificate verification will be disabled. This is problematic as engine.io-client 1.6.8 and earlier passes in an object for settings that includes the rejectUnauthorized property, whether it has been set or not. If the value has not been explicitly changed, it will be passed in as null, resulting in certificate verification being turned off.
- Record
EUVD-2019-0221- Updated
- 2026-11-03
GitHub AdvisoriesGHSA-4r4m-hjwj-43p8
Insecure Defaults Allow MITM Over TLS in engine.io-client
Affected versions of engine.io-client do not verify certificates by default, and as such may be vulnerable to Man-in-the-Middle attacks.
The vulnerability is related to the way that node.js handles the rejectUnauthorized setting. If the value is something that evaluates to false, such as undefined or null, certificate verification will be disabled.
Recommendation
Update to version 1.6.9 or later.
If you are unable to upgrade, ensure all calls to socket.io to have a rejectedUnauthorized: true flag.
- Record
GHSA-4r4m-hjwj-43p8- CVSS 3.0
- 5.9 Medium
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N - Weakness
- CWE-300
- Updated
- 2026-11-02
OSV
engine.io-client is the client for engine.io, the implementation of a transport-based cross-browser/cross-device bi-directional communication layer for Socket.IO. The vulnerability is related to the way that node.js handles the rejectUnauthorized setting. If the value is something that evaluates to false, certificate verification will be disabled. This is problematic as engine.io-client 1.6.8 and earlier passes in an object for settings that includes the rejectUnauthorized property, whether it has been set or not. If the value has not been explicitly changed, it will be passed in as null, resulting in certificate verification being turned off.
- Record
CVE-2016-10536- CVSS 3.0
- 5.9 Medium
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N - Updated
- 2026-11-02
OSVGHSA-4r4m-hjwj-43p8
Insecure Defaults Allow MITM Over TLS in engine.io-client
Affected versions of engine.io-client do not verify certificates by default, and as such may be vulnerable to Man-in-the-Middle attacks.
The vulnerability is related to the way that node.js handles the rejectUnauthorized setting. If the value is something that evaluates to false, such as undefined or null, certificate verification will be disabled.
Recommendation
Update to version 1.6.9 or later.
If you are unable to upgrade, ensure all calls to socket.io to have a rejectedUnauthorized: true flag.
- Record
GHSA-4r4m-hjwj-43p8- CVSS 3.0
- 5.9 Medium
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N - Weakness
- CWE-300
- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
engine.io-clientnpm |
before 1.6.9 | 1.6.9 |
History
| When | Changed | Sources |
|---|---|---|
| 2026-11-03 | aliases | EUVD |
| 2026-11-02 | created | CVE List, GitHub Advisories, NVD, OSV |