Security and anti-patterns¶
Whether you are a system administrator or developer, practicing good infosec hygiene is important. Downplaying the importance of security, whether due to apathy or simply thinking it’s too expensive, can be costly in the long run. This article is meant to briefly touch on some general practices you should follow and is not meant to be a comprehensive guide.
There is no reason not to use HTTPS in 2019. Services like Cloudflare
and Let’s Encrypt offer certificates for free and are easy to deploy.
For Cloudflare, the only thing that’s required is to add some DNS
records and enable universal SSL (with some caveats if you intend on
Full (Strict)). Let’s Encrypt has easy-to-use clients like
certbot that will handle issuing,
revocation and renewal of certificates with minimal interaction.
If you are concerned about speed, see https://istlsfastyet.com/.
For a list of common complaints and rebuttals, see https://doesmysiteneedhttps.com/.
If your complaint is that Let’s Encrypt doesn’t provide Extended Validation Certificates, see Extended Validation Certificates are Dead by Troy Hunt.
There are still some anti-patterns that can limit the usefulness of HTTPS:
If your page redirects HTTP to HTTPS or if you are loading resources
that are HTTP only, your page is still vulnerable. Ideally, you should
combine HTTP Strict Transport Security and
Content Security Policy. For
example, a page which links to a form via HTTP (even if the final
destination is HTTPS) is suspectible to a MITM attack. Mixed content
(loading resources with HTTP even on a HTTPS site) is also an attack
vector. Ensure that you do not allow HTTP requests and that you
whitelist assets to mitigate the damage an attacker can do. At a
minimum, your CSP should include
Using insecure ciphers¶
Allowing insecure ciphers in your suite can expose your users to different types of attacks. There is a trade-off between security and compatibility (and the cipher suite shipped with nginx by the default enables some insecure ciphers). See Mozilla’s Server Side TLS article for a cipher suite that prefers strong ciphers while also taking compatibility into account.
Consider dropping support for obsolete platforms. badssl will test your browser for support for various features.
Consider scanning your server using a third party service like testssl.
Some anti-patterns related to password security include:
Using deprecated hashing functions¶
It goes without saying that you should not be using md5 and sha1 to hash your passwords. While sha256 and sha512 are superior, you should be using a strong hashing function or key derivation function that employs key stretching (the practice of iteratively applying a hashing function) and salting. Both properties will make password hashes more resistant to bruteforcing. For example, bcrypt does this out of the box without need for extra configuration, however key derivation functions like Argon2 and PBKDF2 are also popular choices.  
For services like SMTP, XMPP or PostgreSQL, you should attempt to use SCRAM-SHA1. SCRAM uses PBKDF2 under the hood and is strongly preferred to DIGEST-MD5. The other advantage of this mechanism is that users do not have to store their passwords in plain-text locally.
Arbitrary password lengths¶
If you are storing passwords hashed (which you should), then there is little reason to limit the length of passwords. By definition, hash functions will take an input of arbitrary length and output a string of fixed length. If a site caps password length to a small value (usually something like 16 characters), there is a high probability they are storing passwords in plain-text. However, it is reasonable to cap the password length to something moderately high (like 512 characters) to mitigate denial-of-service attacks. 
It is our opinion that client-side hashing does not add any additional security. The hashed password simply becomes the new password. While one can argue that it obfuscates the original password (since password reuse is rampant), a more effective strategy is to educate users to use password managers and to not reuse passwords across services. There are a few problems with client-side hashing:
- It requires that you trust the client (which is always a bad idea). The user or an attacker can simply modify the client side code to do what they wish. It also makes it easier for an attacker to impersonate the user.
There’s a site (and general opinion) called https://make-linux-fast-again.com/ making the rounds that recommends disabling all mitigations related to Meltdown, Spectre, MDS, et al. It is our opinion that you should not be following this advice. The kernel documentation has pages on L1TF and MDS that discusses these vulnerabilities in full, the available mitigations and the pros and cons of disabling them. In a nutshell, since some of the mitigations lead to performance degradation, some people are suggesting disabling all mitigations. This is very bad advice.
The most significant performance degradation results from disabling SMT. Due to the trade-off between the loss of performance and the low risk of most users being affected by these vulnerabilities, SMT is on by default. If you care about performance, no further action is needed. Disabling the other mitigations exposes yourself to unnecessary risk for little to no performance gain.
Often you will find advice on setting SELinux to
majority of this advice either comes from antivirus vendors or people who do
not want to deal with SELinux errors.
It is our opinion that disabling SELinux to allow an antivirus to work is an oxymoron. While SELinux will not prevent malware from running on your computer, it can mitigate privilege escalation vulnerabilities (for example, see CVE-2019-5736). Because anti-viruses require superuser privileges and conflict with SELinux, they ironically open you up to a whole class of vulnerabilities that anti-viruses will not mitigate.
If you receive an AVC denial, then you should either use
report the bug for your distro so that the maintainers can fix the
policy/module in question. Disabling SELinux wholesale to get an application to
work is never the right answer.
|||See How to securely hash passwords?|
|||See AES: Why is it a good practice to use only the first 16 bytes of a hash for encryption?|
|||See What technical reasons are there to have low maximum password lengths?|