CVE-2017-3737

Description

OpenSSL 1.0.2 (starting from version 1.0.2b) introduced an "error state" mechanism. The intent was that if a fatal error occurred during a handshake then OpenSSL would move into the error state and would immediately fail if you attempted to continue the handshake. This works as designed for the explicit handshake functions (SSL_do_handshake(), SSL_accept() and SSL_connect()), however due to a bug it does not work correctly if SSL_read() or SSL_write() is called directly. In that scenario, if the handshake fails then a fatal error will be returned in the initial function call. If SSL_read()/SSL_write() is subsequently called by the application for the same SSL object then it will succeed and the data is passed without being decrypted/encrypted directly from the SSL/TLS record layer. In order to exploit this issue an application bug would have to be present that resulted in a call to SSL_read()/SSL_write() being issued after having already received a fatal error. OpenSSL version 1.0.2b-1.0.2m are affected. Fixed in OpenSSL 1.0.2n. OpenSSL 1.1.0 is not affected.

How to fix CVE-2017-3737

To remediate CVE-2017-3737, upgrade the affected package to a fixed version below.

• —upgrade to 1.0.2n-r0 or later
• —upgrade to 1.1.0b-2 or later
• —upgrade to 1.0.2l-2+deb9u2 or later

Is CVE-2017-3737 being exploited?

Moderate — EPSS is 42.9%. Track this CVE but it's not at the top of the prioritisation list.

Affected packages (3)

• from 0, < 1.0.2n-r0
• from 0, < 1.1.0b-2
• from 0, < 1.0.2l-2+deb9u2

CVSS scores

References (2)

• ADVISORYsecurity.alpinelinux.org/vuln/CVE-2017-3737
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2017-3737