CVE-2017-3737

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.

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• http://www.oracle.com/technetwork/security-advisory/cpuapr2018-3678067.html
• http://www.oracle.com/technetwork/security-advisory/cpujan2018-3236628.html
• http://www.oracle.com/technetwork/security-advisory/cpujul2018-4258247.html
• http://www.securityfocus.com/bid/102103
• http://www.securitytracker.com/id/1039978
• https://access.redhat.com/errata/RHSA-2018:0998
• https://access.redhat.com/errata/RHSA-2018:2185
• https://access.redhat.com/errata/RHSA-2018:2186
• https://access.redhat.com/errata/RHSA-2018:2187
• https://cert-portal.siemens.com/productcert/pdf/ssa-179516.pdf
• https://github.com/openssl/openssl/commit/898fb884b706aaeb283de4812340bb0bde8476dc
• https://security.FreeBSD.org/advisories/FreeBSD-SA-17:12.openssl.asc
• https://security.gentoo.org/glsa/201712-03
• https://security.netapp.com/advisory/ntap-20171208-0001/
• https://security.netapp.com/advisory/ntap-20180117-0002/
• https://security.netapp.com/advisory/ntap-20180419-0002/
• https://www.debian.org/security/2017/dsa-4065
• https://www.digitalmunition.me/2017/12/cve-2017-3737-openssl-security-bypass-vulnerability/
• https://www.openssl.org/news/secadv/20171207.txt
• https://www.oracle.com/technetwork/security-advisory/cpujul2019-5072835.html
• https://www.tenable.com/security/tns-2017-16