Possible integer overflow in keyboard interactive handling allows out-of-bounds write

Project libssh2 Security Advisory, March 18 2019 - Permalink

VULNERABILITY

A server could send a value approaching unsigned int max number of keyboard prompt requests which could result in an unchecked integer overflow. The value would then be used to allocate memory causing a possible memory write out of bounds error (CWE-130).

There are no known exploits of this flaw at this time.

INFO

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2019-3856 to this issue.

AFFECTED VERSIONS

• Affected versions: all versions to and including 1.8.0
• Not affected versions: libssh2 >= 1.8.1

THE SOLUTION

libssh2 1.8.1 ensures keyboard prompt requests value is less than 100 before proceeding with the login process.

A patch for this problem is available

RECOMMENDATIONS

We suggest you take one of the following actions immediately, in order of preference:

A - Upgrade to libssh2 1.8.1 or later

B - Apply the patch and rebuild libssh2

TIME LINE

It was first reported to the libssh2 project on Dec 3 2018 by Chris Coulson.

libssh2 1.8.1 was released on March 18 2019, coordinated with the publication of this advisory.

CREDITS

Reported by Chris Coulson of Canonical Ltd.