Does `addslashes()` Offer Sufficient Protection Against SQL Injection Attacks?

Understanding SQL Injection Risks through addslashes()

In the realm of PHP programming, safeguarding against SQL injections is a crucial aspect of data security. While mysql_real_escape has gained recognition as a reliable defense, the extent to which addslashes() poses a risk for SQL injections can sometimes remain unclear. This article aims to clarify this by uncovering examples of how addslashes() can contribute to such attacks.

The crux of the dilemma lies in the potential for addslashes() to insert a backslash within multibyte characters. This can disrupt the intended escape sequence, allowing malicious characters to penetrate and manipulate database queries.

To illustrate, consider the following payload:

username = 'lilac\';-- 

If subjected to addslashes():

username = addslashes('lilac\';--');

The result:

username = 'lilac\'\;--'

In this scenario, the intended escape sequence is thwarted, leaving 'lilac';-- as a valid string with an embedded line comment. This comment could be exploited to bypass validation and manipulate the query.

It's important to note that this attack relies on specific character encodings, particularly those with multibyte characters that terminate in 0x5c (backslash). UTF-8, however, is exempt from this vulnerability as its permissible multibyte characters do not conform to this pattern.

Therefore, while addslashes() may serve a role in basic string sanitation, it should not be solely relied upon for preventing SQL injections. The safer approach remains mysql_real_escape, which effectively handles multibyte characters and offers a more robust protection against such attacks.

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