CVE-2017-3738 : Security Advisory and Response

CVE-2017-3738 was published on December 7, 2017, by the OpenSSL Software Foundation. The vulnerability affects OpenSSL versions 1.0.2-1.0.2m and 1.1.0-1.1.0g due to an overflow bug in the AVX2 Montgomery multiplication procedure. This bug impacts processors supporting AVX2 but not ADX extensions, like Intel Haswell (4th generation).

Understanding CVE-2017-3738

CVE-2017-3738 is a carry-propagating bug that poses a potential risk to systems using affected OpenSSL versions.

What is CVE-2017-3738?

The vulnerability stems from an overflow bug in the AVX2 Montgomery multiplication procedure used in exponentiation with 1024-bit moduli. While EC algorithms remain unaffected, attacks against DH1024 are considered feasible, albeit resource-intensive.

The Impact of CVE-2017-3738

Attacks against RSA and DSA are deemed unlikely due to the difficulty involved. However, DH1024 attacks are considered feasible, especially if the server shares the private key among multiple clients.
Processors supporting AVX2 but lacking ADX extensions are vulnerable, such as Intel Haswell (4th generation).
The severity of this issue is low, similar to other related CVEs like CVE-2017-3736 and CVE-2015-3193.

Technical Details of CVE-2017-3738

The following technical aspects are crucial to understanding and addressing CVE-2017-3738:

Vulnerability Description

The overflow bug in the AVX2 Montgomery multiplication procedure poses a risk to systems using affected OpenSSL versions.

Affected Systems and Versions

Product: OpenSSL
Vendor: OpenSSL Software Foundation
Affected Versions: 1.0.2-1.0.2m, 1.1.0-1.1.0g

Exploitation Mechanism

Only processors supporting AVX2 without ADX extensions are vulnerable.
Attacks against DH1024 are feasible, requiring significant resources.

Mitigation and Prevention

To address CVE-2017-3738, consider the following mitigation strategies:

Immediate Steps to Take

Update OpenSSL to version 1.0.2n to fix the vulnerability.
Ensure that servers do not share DH1024 private keys among multiple clients.

Long-Term Security Practices

Regularly update OpenSSL and other software components to patch vulnerabilities.
Implement strong encryption algorithms and key sizes to enhance security.

Patching and Updates

The fix for CVE-2017-3738 is included in OpenSSL 1.0.2n.
Future releases, such as OpenSSL 1.1.0h, will also contain the necessary fixes.